bos: Do encryption if requested

Commit d008089a79 didn't replace the processing of the aencrypt
flag passed to the GetConn() function, causing all bos connections
to be un-encrypted.  This causes "addkey" to fail with an error
from the server, and "listkeys" to silently ignore the -showkey
option to display keys.

Set the AFSCONF_SECOPTS_ALWAYSENCRYPT flag, and don't set
AFSCONF_SECOPTS_FALLBACK_NULL since fallback is not acceptable if
the caller requested enrcyption.

Reviewed-on: http://gerrit.openafs.org/10043
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 7565cb420366d79df319e344678a8d9ceab6db08)

Change-Id: Ibc643a352ed560ad0f32cbff61167463e16201ee
Reviewed-on: http://gerrit.openafs.org/10863
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>