Recover -xe bash option in generatepot.sh

As part of commit 9b939e1b40,
"bash" was added when calling tools/generatepot.sh to avoid tox warning,
but as a result "-xe" option specified at the beginning of generatepot.sh
is no longer considered and we cannot see trace of generatepot.sh
in logs of upstream-translation-update job :-(

This commit explicitly set these options in the shell script
instead of the magic line (line 1).

doc-pot-filter.sh is also updated in the same way.

Change-Id: Ia2ca111cbb386ae5333d8a9a8622f7ac9b19746e

tools/doc-pot-filter.sh

@@ -1,4 +1,6 @@
-#!/bin/bash -xe
+#!/bin/bash
+
+set -xe
 
 #
 # Licensed under the Apache License, Version 2.0 (the "License"); you may

tools/generatepot.sh

@@ -1,4 +1,6 @@
-#!/bin/bash -xe
+#!/bin/bash
+
+set -xe
 
 #
 # Licensed under the Apache License, Version 2.0 (the "License"); you may