OS-270 fixes:

* popen args were not all strings
* Pass original instance and resulting instance IDs in post bless hook.
* Update readme.

Change-Id: Iaa38a10cca58866ab45cf7da1754bb666db10cf3
Merge "OS-270 fixes" into havana/1.5

Conflicts fixed:
	cobalt/nova/extension/manager.py

Change-Id: I19fbd9f704eeab991aea7c0c4f56eead845b0912