Add spec directory contents to test_files gemspec list

This will allow tests to be run on the systems the gem is actually
installed on.

Change-Id: I193908dec9bb7cdbd8d7d0efc21af4deaeb3b348
Reviewed-on: http://gerrit.causes.com/40953
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>