LU-787 clio: ftruncate shouldn't block when grouplock is hold

LU-787 clio: ftruncate shouldn't block when grouplock is hold

Pass the file descriptor used by ftruncate to the CLIO stack so that
ccc_io_one_lock_index() can use the group lock when appropriate (i.e.
when LL_FILE_GROUP_LOCKED is set).

This patch also adds a regression test for this issue.

Signed-off-by: Johann Lombardi <johann@whamcloud.com>
Signed-off-by: Jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Change-Id: I81828cc63bb40586cc1155a58c00e3dab1100ec3
Reviewed-on: http://review.whamcloud.com/2081
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>