LU-927 ptlrpc: common interfaces for ptlrpc_thread::t_flags

LU-927 ptlrpc: common interfaces for ptlrpc_thread::t_flags

Build some common interfaces for ptlrpc_thread::t_flags processing:
thread_is_xxx and thread_yyy_flags. Operating ptlrpc_thread::t_flags
only can through these interfaces.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Change-Id: I285878ffeff8810ecbaf7a42b8d9381f392c0c9a
Reviewed-on: http://review.whamcloud.com/1690
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>