Direct upload of images to swift for Xen

Added support for nova to upload images directly to object store
instead of uploading through glance when using Xen.

Implements bp nova-direct-image-upload

Change-Id: I2a5f36ddbe7a0419779eb054582e9f73df2e1e49
rename image_store

Change-Id: I2cef8f5d72ba0ad757ea3a1bdd4e9c7e5a838ad8
move image handler code to xenapi

Change-Id: Id2c7bdb7b2964a6cf87d4f1ff91effeea9b212f8
test swift store code

Change-Id: Id8547666b161480fa7449a5a10c019ab60a63eff
add glance image handler

Change-Id: Ib812c8311385ee6c25db21fbbaa84643386b7abe
Add error handling logic to swift upload handler

Change-Id: I7cc0c4bb003731fb5b09287885b85a57ec0da9d8
use image upload handlers

Change-Id: Ifb7d489a40b99e1962a572cae6b8abc4476d74c0