shell: reformatted, fixed inspections, typos (#2506)

Reformatted shell scripts according to [ShellCheck](https://github.com/koalaman/shellcheck/).

I. Most common changes:
1. https://github.com/koalaman/shellcheck/wiki/SC2086
	`$var` → `"$var"`
	Note: this isn't always necessary and I've been careful not to substitute where it wasn't necessary in meaning.
2. https://github.com/koalaman/shellcheck/wiki/SC2006
	`` `command` `` → `$(command)`
3. https://github.com/koalaman/shellcheck/wiki/SC2004
	`$(( $a + $b ))` → `$(( a + b ))`
4. https://github.com/koalaman/shellcheck/wiki/SC2164
	`cd "$dir"` → `cd "$dir" || exit 1`
5. https://github.com/koalaman/shellcheck/wiki/SC2166
	`[ check1 -o check2 ]` → `[ check1 ] || [ check2 ]`
6. https://github.com/koalaman/shellcheck/wiki/SC2002
	`cat "${file}" | wc -c` → `< "${file}" wc -c`
	Note: this looks a bit uglier but works faster.

II. Some special changes:
1. In file `utils/common.sh`:
	https://github.com/koalaman/shellcheck/wiki/SC2112
	This script is interpreted by `sh`, not by `bash`, but uses the keyword `function`.
	So I replaced `#!/usr/bin/env sh` to `#!/usr/bin/env bash`.
2. After that I thought of replacing all shebangs to `#!/usr/bin/env bash` for consistency and cross-platform compatibility, especially since most of the files already use bash.
3. But in cases when it was `#!/bin/sh -e` or `#!/bin/bash -eu` another problem appears:
	https://github.com/koalaman/shellcheck/wiki/SC2096
	So I decided to make all shebangs look uniform:
	```
	#!/usr/bin/env bash
	set -e (or set -eu) (if needed)
	```
4. In file `tests/ossfuzz.sh`:
	https://github.com/koalaman/shellcheck/wiki/SC2162
	`read i` → `read -r i`
	Note: I think that there is no need in special treatment for backslashes, but I could be wrong.
5. In file `tests/do.sh.in`:
	https://github.com/koalaman/shellcheck/wiki/SC2035
	`ls *.*cap*` → `ls -- *.*cap*`
6. In file `utils/verify_dist_tarball.sh`:
	https://github.com/koalaman/shellcheck/wiki/SC2268
	`[ "x${TARBALL}" = x ]` → `[ -z "${TARBALL}" ]`
7. In file `utils/check_symbols.sh`:
	https://github.com/koalaman/shellcheck/wiki/SC2221
	`'[ndpi_utils.o]'|'[ndpi_memory.o]'|'[roaring.o]')` → `'[ndpi_utils.o]'|'[ndpi_memory.o]')`
8. In file `autogen.sh`:
	https://github.com/koalaman/shellcheck/wiki/SC2145
	`echo "./configure $@"` → `echo "./configure $*"`
	https://github.com/koalaman/shellcheck/wiki/SC2068
	`./configure $@` → `./configure "$@"`

III. `LIST6_MERGED` and `LIST_MERGED6`
	There were typos with this variables in files `utils/aws_ip_addresses_download.sh`, `utils/aws_ip_addresses_download.sh` and `utils/microsoft_ip_addresses_download.sh` where variable `LIST6_MERGED` was defined, but `LIST_MERGED6` was removed by `rm`.
	I changed all `LIST_MERGED6` to `LIST6_MERGED`.

Not all changes are absolutely necessary, but some may save you from future bugs.

5 files changed, 12 insertions, 12 deletions

diff --git a/packages/ubuntu/debian/postinst b/packages/ubuntu/debian/postinst
index 202f79aa8..fe7f3995c 100755
--- a/packages/ubuntu/debian/postinst
+++ b/packages/ubuntu/debian/postinst
@@ -1,4 +1,5 @@
-#!/bin/sh -e
+#!/usr/bin/env sh
+set -e
 
 case "$1" in
     configure)
diff --git a/packages/ubuntu/debian/postrm b/packages/ubuntu/debian/postrm
index 3347514a1..7a4b65e62 100644
--- a/packages/ubuntu/debian/postrm
+++ b/packages/ubuntu/debian/postrm
@@ -1,5 +1,4 @@
-#!/bin/sh -e
-
+#!/usr/bin/env sh
 set -e
 
 /sbin/ldconfig
diff --git a/packages/ubuntu/debian/preinst b/packages/ubuntu/debian/preinst
index 89699e385..3dd495a35 100644
--- a/packages/ubuntu/debian/preinst
+++ b/packages/ubuntu/debian/preinst
@@ -1,10 +1,9 @@
-#! /bin/sh
+#!/usr/bin/env sh
+set -e
 # preinst script
 #
 # see: dh_installdeb(1)
 
-set -e
-
 # summary of how this script can be called:
 #        * <new-preinst> `install'
 #        * <new-preinst> `install' <old-version>
diff --git a/packages/ubuntu/debian/prerm b/packages/ubuntu/debian/prerm
index 8f91692e0..20a3b0e2a 100755
--- a/packages/ubuntu/debian/prerm
+++ b/packages/ubuntu/debian/prerm
@@ -1,4 +1,5 @@
-#!/bin/sh -e
+#!/usr/bin/env sh
+set -e
 
 case "$1" in
 upgrade)
diff --git a/packages/version.sh b/packages/version.sh
index 1563c7787..957795573 100755
--- a/packages/version.sh
+++ b/packages/version.sh
@@ -1,9 +1,9 @@
-#!/bin/bash
+#!/usr/bin/env sh
 
-SCRIPTPATH="$(cd "$(dirname "$0")"; pwd -P)"
-RELEASE="$(cd ${SCRIPTPATH}; cat ../configure.ac|grep C_INIT|cut -c 20-|rev|cut -c 3-|rev)"
-MAJOR_RELEASE="$(cd ${SCRIPTPATH}; cat ../configure.ac|grep C_INIT|cut -c 20-|rev|cut -c 3-|rev|cut -d. -f1)"
-REVISION="$(cd ${SCRIPTPATH}; git rev-list --all |wc -l | tr -d '[[:space:]]')"
+SCRIPTPATH="$(cd "$(dirname "$0")" || exit 1; pwd -P)"
+RELEASE="$(cd "${SCRIPTPATH}" || exit 1; < ../configure.ac grep C_INIT | cut -c 20- | rev | cut -c 3- | rev)"
+MAJOR_RELEASE="$(cd "${SCRIPTPATH}" || exit 1; < ../configure.ac grep C_INIT | cut -c 20- | rev | cut -c 3- | rev | cut -d. -f1)"
+REVISION="$(cd "${SCRIPTPATH}" || exit 1; git rev-list --all | wc -l | tr -d '[[:space:]]')"
 
 get_release() {
 	echo "${RELEASE}"