Add rxgk client options to vl and pt utilities

Add rxgk client options to vl and pt utilities

Add options to use rxgk for outgoing connections to vlserver, vos,
ptserver, and pts.

For vlserver and ptserver, name the new option -s2scrypt, similar to
the existing volserver option -s2scrypt. For vlserver and ptserver,
specify 'rxgk-crypt' to turn on rxgk crypt connections for our
server-to-server ubik communication.

For vos and pts, just name the new option '-rxgk', and allow the user
to specify the rxgk level to use ('clear', 'auth', or 'crypt'). The
pts code is currently somewhat ill-suited to changing what rx security
class and security level we use, but do the best we can without
refactoring the whole thing.

Change-Id: Iefae46291330d2b5e05b2a2bbaec1b9150b3c892
Reviewed-on: https://gerrit.openafs.org/11105
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: Benjamin Kaduk <kaduk@mit.edu>