Fix a couple bugs in TestCase.create_many_review_requests.
Fix a couple bugs in TestCase.create_many_review_requests.

Our helper to create multiple review requests at once had a few bugs:

* First, the conditional for the `start_local_id` argument was backwards,
  setting the local ID to `None` when a local site was present.
* Second, the code that went to update any existing `LocalSiteProfile`
  counts wasn't properly handling exceptions in the case that the profile
  does not yet exist.
* Third, the summary wasn't being properly formatted with the index,
  leading to all review requests having the same summary "Test Summary %s"

Testing Done:
Ran some unit tests that made use of `create_many_review_requests` with
`with_local_site=True`.

Reviewed at https://reviews.reviewboard.org/r/12687/

reviewboard/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard