1086301: Fix product id product version compare

It was just comparing the version numbers ("5.9")
as numbers. That breaks if you expect "5.11 > 5.9",
so change to use rpm.labelCompare to compare
product cert product versions.

Product version don't necessarily strictly follow
rpm version comparison semantics, but it is a
reasonable and well known algorithm to use for
the default compare.

Add more product version comparison test cases.
Merge pull request #940 from candlepin/alikins/productid_use_rpm_label_compare

Alikins/productid use rpm label compare