cfgfilter: fixup use of testmods

Only one test should ever use each testmod, since they register their
options with a global object and the options are never deregistered.

The testmods with prefix 'f' were added for 'filter' tests, but it
looks like things got a bit screwed up. Keep the 'f' prefixed testmods
for the cfgfilter tests and the other testmods for the config file
generator tests.

Change-Id: Ia7a44a36f5a046fdb4c2f58105229657b0e7e92f
Merge "cfgfilter: fixup use of testmods"