* fix(helm): Use env to locate bash

Leverage '/usr/bin/env bash` for find bash instead of hardcoding
'/bin/bash' since some *nix OSes have it installed elsewhere.
Signed-off-by: Robert James Hernandez <rob@sarcasticadmin.com>

* test(helm): Adding case for versions short flag

When git sha is empty if being built from tarball running 'helm version
--short' should just ignore '--short' since sha is empty. Adding test
to ensure this is the case.
Signed-off-by: Robert James Hernandez <rob@sarcasticadmin.com>

* fix(helm): ignore short flag when sha is empty
Signed-off-by: Robert James Hernandez <rob@sarcasticadmin.com>