Implement vcpu product attribute.

Cores and Sockets are no longer used on virtual guests.
the vcpu attribute is tested against cores
clean up implementation
updated rules.js version, var names, and comments
Added vcpu spec tests
rev rules version to 5.2
add specificity to 'vcpu should be partial' spec test
added test for stackable vcpu subscription healing
Added vcpu managerCapability
Do not check capabilities for the vcpu attribute

This attribute has been used on subscriptions for years, and
we have ignored it until now.  We cannot block subscriptions
from manifest consumers because we've started using the attribute.
Especially considering it will not ever affect physical consumers.
Merge pull request #460 from candlepin/ckozak/vcpu_redux

Implement vcpu product attribute.