get_package_envra: translate missing epochs to '0'
get_package_envra: translate missing epochs to '0'

The query run by get_package_envra() returns a missing epoch as the
string '(none)', but an RPM with no epoch is considered the same (by
rpm.labelCompare()) as having the epoch '0'. Translate so the comparison
functions work properly.

efajardo/osg-test,efajardo/osg-test