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.

ZERO_STRUCTP the info_2 structure before filling it.  Free the device mode
field before freeing the info_2 to avoid a memory leak.  Fixed
uninitialised pointer bug in fill_job_info_2().
(This used to be commit a9547b7e3a068941cda5619f05a64e798584535a)