Fix variable checks in install-deps
Fix variable checks in install-deps

A couple of fixes:
- We check the content of the binary dir as debug step, but this
should be necessary only when in virtualenv.
Also using the correct virtualenv path instead of hardcoding it,
and removing - character after variable name.
- EXTRA_PKG_DEPS is an array and we should treat it like that
when we check if it's empty or not.

Change-Id: I294ef9dce53d7404f4d9285506f1504afabe833f

openstack/bifrost,openstack/bifrost