Fix the authentication prompt appearing multiple times.

The recent change to reorganize how login works (9ab0cac0) actually
broke authentication a bit. RBTools would always prompt at least twice
for a password. This was due to the logic being incomplete and not
actually making use of the new parameters passed in.

This completes that change by adding those parameters instead of trying
for options.username and options.password.
Merge branch 'master' into release-0.5.x
Add support for 2 factor authentication when logging in.

RBCommons will soon be getting 2 factor auth support, and this will
likely trickle down into Review Board at some point once things
stabilize. This change adds support for this when logging into RBTools.

After attempting to log in, the server may respond with an
X-ReviewBoard-OTP header. This is actually quite similar to the
X-GitHub-OTP header that GitHub uses. It indicates that a One-Time
Password is required, and what method the user is expected to use to
receive it. They are then prompted for that password. Once entering it,
RBTools will proceed as before, getting a cookie and using it for future
requests.
Change 'check_install' to take an list of parameters instead of a string.

The 'check_install' method is used to check to see if various command-line
tools we use are present. This method used to take a string and split it on
spaces to get a list of parameters. This seemed an ugly and error-prone way of
breaking things up, so I've changed it to take in a list of parameters instead,
which are passed directly into Popen.

Testing done:
* Ran unit tests.
* Smoke tested rbt.

Reviewed at https://reviews.reviewboard.org/r/5095/