LU-3020 obdclass: Lustre returns EINTR when SA_RESTART is set

LU-3020 obdclass: Lustre returns EINTR when SA_RESTART is set

When Lustre is in a read or write system call and receives a
SIGALRM, it currently returns EINTR at this location. This is
problematic because it prevents the system call from being restarted
if SA_RESTART is set in the handler.

This patch changes behavior in this location to return ERESTARTSYS
when a signal is found.

Signed-off-by: Patrick Farrell <paf@cray.com>
Change-Id: I26e24b8e8e325c5b0bd7d5d20fa97e2180c12263
Reviewed-on: http://review.whamcloud.com/5814
Reviewed-by: Cory Spitz <spitzcor@cray.com>
Tested-by: Hudson
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>