restapi: add storage server connections resource

Several additions to REST api:
1. Add a new root resource for storage server connections.
The new api is http://host:port/api/storageconnections.
2. In backend add getAllServerConnections query class, dao method and stored procedure.
3. Add ability to add (POST) a new storage connection on the resource
mentioned in item 1.
4. Add ability to delete (DELETE) an existing storage connection on the
resource mentioned in item 1.
http://host:port/api/storageconnections/<connectionId>
5. Add ability to update (PUT) an existing storage connection.
Url is the same as item 4, different request type.
6. Add ability to get a specific connection by its id.
Url is the same as item 4.
7. REST unitests
8. add feature to rsdl
9. host details providing is optional,
will lead to connectivity attempt to storage in vdsm.
Feature page:
www.ovirt.org/Features/Manage_Storage_Connections

Change-Id: If6bc32ead098390723825872f6fb292097d52835
Signed-off-by: Alissa Bonas <abonas@redhat.com>