staging: lustre: improve waiting in sptlrpc_req_refresh_ctx

Replace l_wait_event with wait_event_idle_timeout() and call the
handler function explicitly.  This makes it more clear
what is happening.

Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: Patrick Farrell <paf@cray.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>