DigitalOcean: Add configuration for state timeout

The state_timeout config allows you to determine the timeout
for "waiting for droplet to become [active, off, etc.]".

This still defaults to 3 minutes.

I ran into a few cases where the droplet was active and a TCP connection
could be made, but SSH wasn't running yet and the handshake failed. A
race condition with the machine boot. This will retry the SSH handshake
a few times.

/cc @pearkes