clear form for user who needs to enter a new repository title & short name that hasn't already been taken

[hannahfrost]

While creating a new repository tenant, if the title or short name that I enter has already been used, in addition to getting a message about the conflict, the form changes. The title field in the form is cleared, but not the short name. Based on testing, this seems to be case regardless if the title is the conflict or the short name is the conflict.

In either case, it would be would be better to clear out both fields for the user to enter a new title and short name combination.

[mjgiarlo]

Blocked by #647

[mjgiarlo]

@atz Still in progress, or should we shunt it onto the backlog?

[atz]

@mjgiarlo Should just merge this with the other repo creation ticket (#649). I cannot seem to cause collision in the demo site, oddly.