This patch rewrites the following functions
    *vboxStorageOpen
    *vboxStorageClose
    *vboxConnectNumOfStoragePools
    *vboxConnectListStoragePools
    *vboxStoragePoolLookupByName

These functions do not call any vbox API, so I directly move it
from vbox_tmpl.c to vbox_storage.c

A small improvement is made on vboxConnectListStoragePools.
The if condition nnames == 1 is modified to nnames > 0. So if the
caller put more than one slot to get active storage pools, the new
function will return exactly one, while the old one would only
return 0.