handle unexpected power state change correctly

If power state of VE is change from outside the OpenStack,
it handles it with some logic: if VE is unexpectedly running
or suspended - it calls power_off method. If it is unexpectedly
running - it also calls power_off. We don't know, how if this
logic will be changed or not. So let's always set requested
state without making assumptions about current state.
update requirements.txt from nova's repo
utils: add PloopMount class

Add class PloopMount for assembling ploop devices
from images.
implement injecting data into images

Use virt.disk to inject admin_pass, files, ssh keys
into new instance's root fs.

The code is partly taken from the libvirt driver.