Adds retry/backoff behavior to the policy engine feed sync checker to handle bootstrap better
Adds retry/backoff behavior to the policy engine feed sync checker to handle bootstrap better

The handler that checks to ensure a task is queued may fail during system startup if the queue service is not yet available
in this case it is better to backoff and retry the queue operation a few times before waiting for the next duty cycle, which is
typically configured to be many minutes or hours.

This fix adds simple retry and backoff that has some environment variable overrides:
ANCHORE_FEED_SYNC_CHECK_RETRIES to set the number of retries (an int), default = 5
ANCHORE_FEED_SYNC_CHECK_FAILURE_BACKOFF to set the second of backoff between retries (an int), default = 5

Signed-off-by: Zach Hill <9de8c4480303b5335cd2a33eefe814615ba3612a@anchore.com>

anchore/anchore-engine,anchore/anchore-engine,anchore/anchore-engine