961003: Stricter matches for rhel product tags

Fix cases where we wont delete product certs
for "rhel-6-server-highavailability" since we think
that is a rhel base os product.

Split out the tag matcher to it's own class, and
switch to a regex implementation. Add test
cases for class.
Merge pull request #891 from candlepin/alikins/961003_productid_ha_not_rhel

961003: Stricter matches for rhel product tags