Revert "crowbar_join: Get the hostname before pinging the admin server"

This reverts commit f0185a468010a492d23af774a68ee09fd6109233.

If we can't ping the admin, then really, we're done. No need to enter a
loop for the hostname.
crowbar_join: Reduce time of loop for hostname

There's no point in waiting 10 minutes. If it's not there after one
minute, let's give up.
Merge pull request #307 from vuntz/crowbar_join-ping-early

Avoid uselessly long loop when waiting for hostname