(PUP-3248) Fix PMT tests for directory environment

The beaker host['distmoduledir'] variable is not meaningful if the
host is using directory environments (e.g. 'production').

This commit updates the helper methods for validating that a module
is (or is not) installed on the host by iterating over the
modulepath if a specific modulepath is not provided.

The calls to these helper methods have been updated for the change
in parameter ordering in the helper methods.
So I think this just needs to change to:

"environmentpath", ""

(and we can get ride of the envpath variable lines above that)