1025044: fix cores pre-entitlement calculation

cores pre_entitlement check was not properly multiplying
cores_per_cpu by sockets. This caused us not to filter
some subscriptions from list available that we should.

Added tests for other pre_entitlement attribute warnings
as well
Merge pull request #423 from candlepin/ckozak/fix_cores_pre_entitlement

1025044: fix cores pre-entitlement calculation