Rework the ugen_* interface

Rework the ugen_* interface

Remodel the ugen_* ubik initialisation interface so that more complex
sets of security flags can be passed through it. A number of new
functions are provided, all of which take the AFSCONF_* security flags
defined in libauth:

*) ugen_ClientInitCell is used to initialise a ubik client structure
   when the caller already has afsconf_dir and afsconf_cell
   structures for the cell being contacted
*) ugen_ClientInitServer is used to initialise a client which will
   contact a specific server within a given cell, rather than
   selecting one from the pool
*) ugen_ClientInitFlags is used to initialise a client given a
   cellname, and a path to a configuration directory. It is is
   closest to the legacy ugen_ClientInit function.

All of the in tree callers are updated to use this new interface

Change-Id: I6a438aa70d94114c8b6626fa1396b7580ab07c07
Reviewed-on: http://gerrit.openafs.org/7131
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>