Check if VM info has extra info before we use it
Check if VM info has extra info before we use it

This was causing some NoMethodErrors if instance['extra_info'] was nil, which can
happen if a VM is started with no startup info, for instance if one is manually
started to debug something.

final-ci/travis-worker,ireznice/travis-worker,final-ci/travis-worker,travis-ci/travis-worker,ireznice/travis-worker,travis-ci/travis-worker,gavioto/travis-worker,gavioto/travis-worker