libvirt: remove hack from ensure_filtering_rules_for_instance

The ensure_filtering_rules_for_instance method had a hack
where the test suite caller could pass in a module to
replace the greenthread.sleep call. This is utterly crazy
when mock can trivially replace the greenthread.sleep call
directly.

Partial-bug: #1333219
Change-Id: I449290aa366f5c85cc63a15d0b1704339be4d73a
Merge "libvirt: remove hack from ensure_filtering_rules_for_instance"