what is the default session retry policy

**QUESTION**

it seems AuditorElector do not set the session retry policy

our zk ticktime is 2s

and zkTimeout=30000 in bk

if there is a gc occurs in zk, bk will failed .

The report names AuditorElector, zkTimeout=30000, and a 2s ZooKeeper tickTime, but no file or test. Start by locating AuditorElector's session setup and tracing how the default retry policy is selected; done means documenting the default and explaining or reproducing the GC-related failure.

Written by the indexing model from the issue text.