Import and use units constants in the test to improve
readability.

Signed-off-by: Albert Esteve <[email protected]>

Fix small typo on extents example.

Signed-off-by: Albert Esteve <[email protected]>

Report image virtual size in OPTIONS so clients can get the image size
without a possibly slow extent call.

Report the format since OPTIONS can report the virtual size only when
the backend provides raw format. This is used when using the http
backend to report OPTIONS to the client.

Reporting virtual size is easy with the nbd and memory backends since
they always use raw format.

When using file backend and qcow2 image, we don't have access to the
image virtual size, and this size is not helpful to the user uploading
or downloading data. Currently we don't know about the image format
since engine does not report it in the ticket.

The http backend reports the info from the remote server, so it depends
on the backend used by the remote server, and on having new server
reporting the format and size.

To keep code and the API simple, we report virtual size only when using
the nbd and memory backends. When engine will report the image format
for the file backend, we can also report the size for raw images access
via the file backend.

Change-Id: I89118301c98dc2d11c25a4d1e7ef83df26336f01
Related: oVirt#67
Bug-Url: https://bugzilla.redhat.com/1924945
Signed-off-by: Nir Soffer <[email protected]>