Windows: Move GetAuthenticationId to Worker Thread

Windows: Move GetAuthenticationId to Worker Thread

When PsReferenceImpersonationToken(), PsReferencePrimaryToken(), and
SeQueryInformationToken() are called in the kernel from a user process
thread the restrictions on the userland process still apply.  Since we do
not want to be restricted we must obtain the token and query the token
information from a SYSTEM thread.

This change restructures the AFSGetAuthenticationId() process to queue a
synchronous task to the worker thread.

This should address the problem that has been seen during system boot when
the Group Policy Service attempts to query, remove or create a drive
letter mapping.

Change-Id: Ib8772e185aa1e4e52979ec847bbc18a9878bcaca
Reviewed-on: http://gerrit.openafs.org/11909
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>