Polling repositories should us a back-off strategy if the repository is unavailable.

We moved the repository location for a Git repository but all the branch builds still point to the old location (see BAM-12330).

Bamboo keeps polling that repository for all those branch builds even though it's gone. It would be nice if Bamboo has a back-off strategy that decreases the frequency of the poll operations and eventually gives up if the repository cannot be reached.