Unify `-eu' shell attributes in cartridge scripts

Fail on errors:
- `set -e' by default
- `set +e' should be enabled explicitely for a certain sequence of
commands only

Fail on unset variables:
- `set -u' by default
- `set +u' should be enabled explicitely for a certain sequence of
commands only

https://bugzilla.redhat.com/show_bug.cgi?id=1168512
Fix unbound variables in cartridge scripts