Increment the instruments retry loop counter _after_ it's used.

Previously, we'd skip the first value of the launch timeouts array (30)
and then use a value beyond the array's length, as can be seen in
https://travis-ci.org/inkling/Subliminal/jobs/21707856.
Merge pull request #156 from inkling/jeff/correct_instruments_retry_count

Increment the instruments retry loop counter _after_ it's used.