Fix shell scripts to run correctly on Debian

Temporarily change shebang to /bin/bash in scripts that depends on bash
extensions.

Also corrects a few 'exit -1' in netns/*.sh scripts.

Signed-off-by: Joseph Beckenbach <jbeckenbach@lancope.com>
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>