Remove expectations on nil warnings

When running all rspecs somewhere in the middle were displayed warnings
that you are expecting message receive on nil objects. This was caused
by wrong variable names in systems_controller_spec.
Fix ping spec

Headpin ping spec was not set in headpin mode so it tried to contact
Pulp. I DRYed up this spec and added config stubbing so it works
correctly.
add ruby193-rubygem-ruby-rc4 to comps
Merge pull request #1675 from ares/tdd/ping_test_fix

TDD: Fix ping spec
Merge pull request #1674 from ares/tdd/remove_spec_warnings

TDD: Remove expectations on nil warnings