powertest.py should call replSetReconfigure command only after successful replSetGetConfig

replSetReconfig is not safe to retry when there's an AutoReconnect error. If it succeeded before the network was disconnected, it will likely fail the retry.

I believe it is safe to retry the whole else-clause starting with replSetGetConfig

https://github.com/mongodb/mongo/blob/1d89d2c88bcb39045701b87612b866ae2eb49378/pytests/powertest.py#L1440

In this case, if the previous reconfig succeeded, the "if" at line 1457 will prevent attempting to reconfig again.