Improved boot from volume

In connection to blueprint:
https://blueprints.launchpad.net/nova/+spec/improve-block-device-handling
and extension of nova boot functionality (Image Clone), we propose optimaze
web-interface of launche VM instances and reflect new Nova functionalities.

Tab "Volumes" was moved to "Details" and called as "Instance Boot Source"
section in the "Launche instance" pop-up window.
The field "Instance Boot Source" contains following options:
- Boot from image.
- Boot from snapshot.
- Boot from volume.
- Boot from image (creates a new volume).
- Boot from volume snapshot (creates a new volume).

For option "Boot from image (creates a new volume)" we added new field
"Device size (GB)", to determine size of volume. It's required for Nova.

Implements: blueprint improved-boot-from-volume

Change-Id: I92ee5704d70c32b2c73c60c4d424d7d6d320ab24
Merge "Improved boot from volume"