Adds max-backoff for retries in Connection.

The max-backoff concept prevents the backoff used in _retry to double infinitely (which in turn causes wait times of an hour or more between retries).

As per review, changed code to use min instead.

Fixes: bug #1183542

Change-Id: Ic084f54069b7fa7a33604741487045c5e697ff06
Merge "Adds max-backoff for retries in Connection."