Add power management support to register nodes.

This changes makes it possible to pass real pm_address, pm_user, and
pm_password parameters to the nova baremetal-node-create commands.

To use simply pass PM_IPS, PM_USERS, and PM_PASSWORDS parameters
(space delimited) so that the associated user:password combination
correspond to the MACS (which we already require to use this script)

The motivation for this change is to make it possible to use this
script (and follow the dev/test story) using *real* hardware and
not just fake VMs.

Change-Id: I347edeb3b81473305d64f74ea2ac78d731361c9d
Add doc note about over-mtu packet loss.

In some cases (on Fedora 19, using *real*
bare metal, etc) users have seen over-mtu packet
loss when running iSCSI commands. In these
cases:

  iscsid: log shows repeated connection failed errors (and reconnect)

  dmesg shows:
    openvswitch: vnet1: dropped over-mtu packet: 1502 > 1500

This patch makes a note in devtest so that people who encounter
similar errors may know they need to increase their MTU
for the control plane.

Change-Id: Iefdb0ab31769bc0a9cd15eab3948f3d78c35efdd