Introduce the Gluster storage type

Introduce the Gluster storage type

Currently, the 'gluster' and 'sharedfile' disk templates are both mapped
to the Shared File storage type. This compromise causes the Gluster block
devices to be interpreted in the config as 'sharedfile' devices, instead
of 'gluster', and subsequently to be wrongly handled as Shared File
disks. This behavior, currently makes the 'gluster' disk template not
functional.

This patch, fixes this issue by introducing the Gluster storage type,
which will be exclusively used by the 'gluster' disk template.

Signed-off-by: Dimitris Bliablias <bl.dimitris@gmail.com>
Signed-off-by: Petr Pudlak <pudlak@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>

Cherry-picked from ba550291df12b129f843581c098b3896023e7d33

Signed-off-by: Lisa Velden <velden@google.com>
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>