Update tests to be compatible with busted v2.0

In busted v2.0 _TEST is no longer defined, so it must now be explicitly
set in the tests. In addition, the global 'arg' variable must be set via
the '_G' table, otherwise it is not visible to 'cli:parse'.
Support alternate --expanded-key notation w/o '='

Allow the '=' in expanded-key notation to be optional such that the
following will work:

	--expanded-key VALUE

Of course using the '=' is still valid, as --expanded-key=VALUE will
still work.