Perforce allows administrators to configure the repository name into the

p4 counters. This was then used in the case where the name was not

already provided from the config or command line options. Unfortunately,

this was stuck into the RepositoryInfo structure, which wasn't the best

place for it. This also meant that even when the repository name was

configured in .reviewboardrc, we'd query the p4 counters looking for it.
This change moves the repository name out of the RepositoryInfo

structure and into a method which is only called if the repository name

is not provided in another way. It also actually uses that name when

querying the repositories inside the get_repository_id method (as

opposed to fetching all repositories and then comparing against the

name).

Ran unit tests.
Verified that get_repository_id was now only fetching a single

  repository from the API during commands such as rbt status and

rbt post -u.