Backoff when minion fails to connect

NOTE: This is a potential change --- I haven't actually gotten a
test environment to try this out.

This adds a configuration option to the minion,
`acceptance_wait_time_max', that if set changes the acceptance
wait loop to add `acceptance_wait_time' seconds to the wait between
each iteration, up to this maximum value.

POTENTIAL FIX: Issue #5813
Merge pull request #6360 from kula/fix_5813

POTENTIAL FIX: Backoff when minion fails to connect