Avoid excessing logging of RetryRequest exception
Avoid excessing logging of RetryRequest exception

Such exception indicates of error condition only if
retries are exceeded. In other cases error-level logs
pollute the log file and complicate log analysis.

Change-Id: I318867043a68a6499851631593859a0fffac6038
Closes-Bug: #1433001

openstack/oslo.db,openstack/oslo.db,magic0704/oslo.db