Fix hosting service bug tracker configuration and required flags.

Bug tracker configuration had some problems when using the hosting
service's bug tracker, especially with certain combinations of bug
trackers and hosting services.

There were two key issues:

1) The bug tracker plan field's required state was based on the selected
   bug tracker service, but it wasn't taking into account the Use
   Hosting Service's Bug Tracker state. Now that is factored in.

2) The bug tracker plan's value wasn't being based off the repository
   plan when using the hosting service's bug tracker. This meant that if
   you used GitHub as the hosting service, the bug tracker plan was
   still "default", which didn't exist in the GitHub hosting service's
   plans. Now that's using the selected hosting service's repository
   plan.

While working on this, I realized that we were doing a lot of work to
set the required flags, but never setting them back, which made them
appear incorrectly (which could possibly affect validation on future
fixes). So now we store the required states and then set them back after
validation.

To make the unit tests for this not be so time-consuming, I added a flag
to turn off the repository validation. This is used in the new test for
bug trackers.

New unit tests run, and the repository I was trying to configure now works.