(maint) Use same prioritizer throughout catalog

Under normal system runs, there wasn't any problem with the prioritizer
being used, since the Puppet::Resource::Catalog created it and passed to
all of the correct places. However, the testing methods in
PuppetSpec::Compiler ended up lying to the user about the prioritizer
that could be used. The prioritizer that was passed in was not the one
actually used by the catalog for constructing the relationship graph.
This was because the Puppet::Parser::Catalog used the one it had
internally. The answer is to have the Puppet::Parser::Catalog act as one
possible factory of prioritizers, and pass the prioritizer around as it
needs it. This allows the tests to then pass in the correct prioritizer
and use it consistently throughout.