Wait for heat-admin to be configured on undercloud

cloud-init configures the heat-admin user after ssh comes up, if things
happen fast enough when init-keystone tries to ssh to the undercloud it
may stall while ssh waits for a password to be entered. We need to wait
for the ssh key to be in place.

Change-Id: I87edb55a38f2a3e21e1653e57e9849e971ba02c8
Merge "Wait for heat-admin to be configured on undercloud"