Parametrize suppress_auth_failure & report auth failures by default

This would likely be a breaking change, but as of version 0.6.0 of this gem, auth failures are not reported properly and result in a loop of:
Waiting for remote response before bootstrap.DEBUG: Adding <snip_IP>
DEBUG: :session => :init
DEBUG: :relay_to_servers => echo . & echo Response received.
DEBUG: :relayed => <snip_IP>
DEBUG: 172.28.0.85 => :run_command
..DEBUG: Adding <snip_IP>
DEBUG: :session => :init
DEBUG: :relay_to_servers => echo . & echo Response received.
DEBUG: :relayed => <snip_IP>
DEBUG: 172.28.0.85 => :run_command
.

This PR adds a --suppress-auth-failure flag that when passed, emulates the previously default behaviour.