lib: Fix server_id_from_string

lib: Fix server_id_from_string

sscanf overwrites vars as numbers come in. So the first sscanf will
overwrite "vnn", although it can't scan the whole thing. This leads
to the string "1234" return .vnn=1234, pid=1234. Bad.

While there, save the temp variables. The SCNu32/64 thingies look
ugly, but it's actually c99.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>