Small style cleanups / resolve rubocop warnings
Allow multiple package prefixes to be specified

Some tags specify the 'rubygem-' prefix while others specify
'ruby193-rubygem-'. This allows us to query both at the expense
of additional query time
Add spec testing multiple package prefixes
Merge pull request #86 from ManageIQ/logging-followup

Small style cleanups / resolve rubocop warnings
Merge pull request #87 from ManageIQ/multiple_prefixes

Multiple prefixes
Expand polisher errors, raise errors on various edge cases (rev 2)

Some refactoring including expansion of ConfHelpers module
and reorganizing Polisher::Gem#versions. Specs added to test
the later (and gem_dependency_checker verified)

Revised to rebase against master & fix style issues