Add volume_glance_metadata to volume.api.get

The dict(rv.iteritems()) agains the volume object from
volume.api.get does NOT set the volume_glance_metadata k/v.

This is used to show bootable in the show and list api calls,
the result was that list properly reflected the bootable status
of a volume, however show would always describe the flag as False.

So we simply check if the rv includes the glance_metadata and if
so go ahead and create the entry in the volume dict.

Fixes bug: 1115629

Change-Id: Ia0be08f3d2c85b7fe8390fca264803c96cdce7f7
Merge "Add volume_glance_metadata to volume.api.get"