LU-3808 ptlrpc: Return a meaningful status from ptlrpcd_init()

LU-3808 ptlrpc: Return a meaningful status from ptlrpcd_init()

This patch has the following:
1) Fix for the return value from ptlrpcd_init(). It will now return a
correct status instead of returning zero always.
2) ptlrpcd_addref() should not increment ptlrpcd_users on error.
3) Added code in a mdc_setup() and mgc_setup() to test the return
value of ptlrpcd_addref() and return on error.

Signed-off-by: Swapnil Pimpale <spimpale@ddn.com>
Change-Id: I684b5603b33d469f4e7566d07f52cb49b05c8ec6
Reviewed-on: http://review.whamcloud.com/7522
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>