TT#32956 Do not ignore errors from maintscripts

Change-Id: Id3f3c2c49d18d1a8dbe2ded9f7b7cde5c53e0fc6

debian/ngcp-system-tests.postinst

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -e
+
 # Remove obsolete files generated from templates.
 rm -rf /etc/ngcp-tests/ce
 rm -rf /etc/ngcp-tests/pro

debian/ngcp-system-tests.postrm

@@ -1,4 +1,4 @@
-#!/bin/sh -e
+#!/bin/sh
 # This script can be called in the following ways:
 #
 # After the package was removed:
@@ -26,6 +26,8 @@
 # If preinst fails during upgrade:
 # <new-postrm> abort-upgrade <old-version>
 
+set -e
+
 case "$1" in
   purge)
     rm -rf /etc/ngcp-tests/