Fix perforce options access.

Not all rbt commands add the perforce command-line options, but the p4client
was accessing them as if they did. Trivial fix.
Switch to fuzzy search in setup-repo to match repository path.

Sometimes repository path on reviewboard server and on local copy of repository
may contains slight difference (trailing slash, user credentials, etc.) Now rbt
setup-repo offers repository with closest path to local path.

Testing done: Ran unit tests.

Reviewed at https://reviews.reviewboard.org/r/5724/
Merge branch 'release-0.6.x'