Make virtual power ssh pubkey world readable.

On undercloud nodes we connect as heat-admin, not root, so we need a
non-root access path or we can't enable the power manager to login and
talk to libvirt.

The code was also a little messy, so tidied up the immediate context.

Change-Id: I2e2cb487cee64736ff1b5184e52b1ffd0e4620ad