[PATCH-v2] Add the write error handling to cg_set_control_value().

[PATCH-v2] Add the write error handling to cg_set_control_value().

Changelog since v1:
 o Use fopen/fprintf/fclose instead of open/write/close.
 o Add the error handling against fclose.

cg_set_control_value() is the function for setting a value to a file
of cgroup file system. And current function does not handle the error
of writing to a file. So we cannot know whether setting value is
enable or not. This patch add the error handling for knowing it.

Signed-off-by: Ken'ichi Ohmichi <oomichi@mxs.nes.nec.co.jp>
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>