(MAINT) Mergeback 0.7.3 Release

Prior to this commit the safety check in the canonicalize method intended to prevent
multiple executions to canonicalize the same resource compared the cached resources
to the *full* resource being checked; this commit changes that check to only search
for a hash containing the matching namevars.

This should prevent multiple runs and bugs where mandatory parameters are dropped
during an RSAPI refresh event.

…ical-cache-on-namevar

(GH-105) Ensure canonicalized_cache check validates against namevar

Prior to this commit if a resource is ensurable but the value of ensure on
the target node was not Present or Absent the call to run Invoke-DscResource
never gets made.

This commit updates the logic in the set method to call update() if the state
of the ensurable resource is ambiguous from a CRUD perspective, which is
preferable to not running set at all.

…-on-ambiguous-ensure

(GH-105) Ensure set runs on ambiguous ensure states

(MAINT) Prep for 0.7.4 release