staging: lustre: remove 'ptlrpc_thread usage' for sai_agl_thread

Lustre has a 'struct ptlrpc_thread' which provides
control functionality wrapped around kthreads.
None of the functionality used in statahead.c requires
ptlrcp_thread - it can all be done directly with kthreads.

So discard the ptlrpc_thread and just use a task_struct directly.

One particular change worth noting is that in the current
code, the thread performs some start-up actions and then
signals that it is ready to go.  In the new code, the thread
is first created, then the startup actions are perform, then
the thread is woken up.  This means there is no need to wait
any more than kthread_create() already waits.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>