Work around RHEL/CentOS 7 command completion issue.
There is a known issue with 'set -u' in CentOS 7
interfering with command line completion in interactive
shells. It goes totally bonkers when you try a tab
completion. We use 'set -u' as a good programming
practice; it declares bash variables to be declared
before being referenced. But it's not really needed
in interactive shells. It's not an issue in CentOS 6.
I was hoping this would get fixed in RHEL/CentOS, but
it's not as of CentOS 7.3.
One workaround would be to remove 'set -u' from p4_vars,
and instead set it in all scripts instead. That way
it is always set for programming, and not set when
p4_vars is sourced for human interactive use.