s3-rpcclient: add fsrvp commands

s3-rpcclient: add fsrvp commands

fss_create_expose connects to an FSRVP server and negotiates the
creation and exposure of a share shadow-copy.
shadow-copies of multiple shares can be requested with a single
fss_create_expose request.

ddiss@plati:~> bin/rpcclient -k -U 'LURCH\administrator%password' \
                             ncacn_np:lutze[sign]
rpcclient $> fss_create_expose backup ro hyper
381884f2-b578-45ea-b8d2-cf82491f4011: shadow-copy set created
...
share hyper@{B6137E21-9CBB-4547-A21D-E7AD40D0874B} exposed as a snapshot
of \\lutze\hyper

fss_delete removes the shadow-copy share:
rpcclient $> fss_delete hyper 381884f2-b578-45ea-b8d2-cf82491f4011 \
                        b6137e21-9cbb-4547-a21d-e7ad40d0874

Shadow-copies can be created read-write or read-only.
Experimenting with Windows Server "8" beta, a recovery complete call is
required after creating a read-write (ATTR_AUTO_RECOVERY) shadow copy.
Otherwise subsequent creation requests fail with
FSRVP_E_SHADOW_COPY_SET_IN_PROGRESS.