register plugin path issues

[hannesdelbeke]

created a register path test while working on previous PR
and noticed odd behaviour, described in issue #379

this new test influences test behaviour of unrelated tests

in py2 and py3
a test that should fail or be skipped, does not run
This came to my attention while working on pathlib deregister support #384 .
The deregister path test stopped running when adding this new binary string test.
The test is not skipped, and did not fail, it inexplicably wasn't picked up by nose.
When removing the new test commited in this PR it worked again.

we can see this reflected in the logs https://ci.appveyor.com/project/mottosso/pyblish/builds/42230403/job/oefioqph7sbsnbqn
pathlib deregister test does not run

issue when using binary string to register plugin paths

in py 3
binary string fails in py3+

register the following path

u"c:\some\special\södär\testpath".encode('utf-8')

results in failed test
AssertionError: b'c:\some\special\s\xc3\xb6d\xc3\xa4r\testpath' not in ['C:\\projects\\pyblish\\pyblish\\plugins', 'server\\plugins', b'c:\\some\\special\\s\xc3\xb6d\xc3\xa4r\testpath']

see old PR #383 for more info