LU-9771 clio: introduce CIT_GLIMPSE for glimpse

LU-9771 clio: introduce CIT_GLIMPSE for glimpse

It turned out that it's better to have a standaline I/O context
for glimpse request. In that case, it's easier for glimpse to try
a new mirror if the current one is out of access.

Another problem in this patch is to zero cl_io data structure if
the I/O starts from OSC layer.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ieeac36d4af38bc04a01affb9e6d3d129bceeb74e
Reviewed-on: https://review.whamcloud.com/29082
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>