storage: Complete implementation volume by hash object

storage: Complete implementation volume by hash object

Alter the volume logic to use the hash tables instead of forward
linked lists. There are three hash tables to allow for fast lookup
by name, target.path, and key.

Modify the virStoragePoolObjAddVol to place the object in all 3
tables if possible using self locking RWLock on the volumes object.
Conversely when removing the volume, it's a removal of the object
from the various hash tables.

Implement functions to handle remote ForEach and Search Volume
type helpers. These are used by the disk backend in order to
facilitate adding a primary, extended, or logical partition.

Implement the various VolDefFindBy* helpers as simple (and fast)
hash lookups. The NumOfVolumes, GetNames, and ListExport helpers
are all implemented using standard for each hash table calls.