Simplified server pipe implementation by changing arguments passed down

Simplified server pipe implementation by changing arguments passed down
through to the individual pipe api calls.  Instead of passing two
prs_struct pointers, we now pass the pipes_struct pointer which contains
the former information as well as other useful stuff like the vuid.

Pass the vuid from the pipes_struct down to the lower level spoolss
functions to perform security checks.
(This used to be commit f6436aacd631abeda60b87d671993f9e426cc684)