Remove `utils.debug`

Hasn't been used in years.

Change-Id: Ia3f14adbdfaa122d49f550263d03eceabdfc34a4
XenAPI: Add versioning for plugins

Because the plugins live on a host seperate to Nova we need an interface
to test whether they are the expected version.  We can't use pip or other
requirement systems as they are cross-machine.

Closes bug 1226622

Change-Id: I58ab669061f51bd87071e2cf0d93d33021001309
Avoid mutable default args in _test_populate_filter_props

Using [] as an argument means that any changes to that argument
will stick across multiple calls to the method.  In this case,
this is surprising behavior that may lead to confusion as we
reuse this method in more tests.  Instead, set it to None, which
is non-mutable, and later assign it to [] inside method scope.

Change-Id: I9cc07b8917ad096c5efea9282bae08c41d15f1cf
Merge "Avoid mutable default args in _test_populate_filter_props"
Merge "Remove `utils.debug`"