devtest: prepend scripts dir to $PATH

I had an older version of python-keystoneclient installed in /usr and
everything was broken because e.g. 'keystone role-get admin' doesn't
work with that version.

Change-Id: Ifa32ae1245b69fffee60c0ef1d8013b964347868
Ensure demo user password is in overcloudrc-user

We're now generating a password for the demo user in the overcloud but
we're not including it in overcloudrc-user.

Change-Id: I2efb3b80df0aace90f2da501f839fe2f66141a9d
Create baremetal nodes and register them in lockstep

It's pretty confusing that we create 3 baremetal nodes towards the
beginning of the instructions, add 1 to the seed cloud and then
later add the other 2 to the undercloud.

We can easily create the required number of new nodes and immediately
register them when they're needed.

This makes it a lot more clear what you need to do if you want to
recreate just the baremetal node for running the undercloud.

Change-Id: I9e669c83fb9403acf939458afa8fcf2d27d18f5e