Baremetal: Be more patient with IPMI and BMC

Before we called 'power status; power on' in a loop which made the
IPMI/BMCs not behave well.  Also the total time we would wait (2.5
seconds wasn't always enough).  So make sure power on/off is only called
once and wait up to 10 seconds for the power state change to go into
effect.

This patch has been tested on real baremetal using
https://wiki.openstack.org/wiki/TripleO/TripleOCloud

This bug is also linked to ironic so the change will be made there as
well.

Change-Id: I5a4d7c84ebdf9c1f7d8d0570dbc31764c31f1fc6
Closes-Bug: #1234479
(cherry picked from commit 6e30bbc126a1ad4eb87e735c812832f4fcc0054e)
Merge "Baremetal: Be more patient with IPMI and BMC" into milestone-proposed