Enable RBD backend for location option

Currently only 's3', 'swift', 'http' are supported with the --location option of glance client. It's not that difficult to implement it with an RBD backend, simply change the line 278 form the file /glance/api/v1/images.py with:

 for scheme in ['s3', 'swift', 'http', 'rbd']:

It seems to be working for me after the change:

$ glance image-create --size 2147483648 --name ubuntu-rbd-hack --store rbd --disk-format raw --container-format ovf --location rbd://ubuntu-raw
+------------------+--------------------------------------+
| Property | Value |
+------------------+--------------------------------------+
| checksum | None |
| container_format | ovf |
| created_at | 2013-05-06T15:29:26 |
| deleted | False |
| deleted_at | None |
| disk_format | raw |
| id | 0d47c421-b079-44ff-bcc5-ee711d500512 |
| is_public | False |
| min_disk | 0 |
| min_ram | 0 |
| name | ubuntu-rbd-hack |
| owner | 19292b3b597b4ecc9a41103cc312a42f |
| protected | False |
| size | 2147483648 |
| status | active |
| updated_at | 2013-05-06T15:29:26 |
+------------------+--------------------------------------+

The only thing I noticed, is that I might have raised another (bug?) not implemented feature here:

Skipping store.set_acls... not implemented. set_acls glance/store/__init__.py:304

It seems to be harmless but this might lead to another bug report, what do you think?

Thanks.