Quick bug fix for missing fd for move_in_cgroup

There is an issue where if the proccess to be killed spawns a child proccess and
moves it in a child cgroup of the one the parent process is in, the cgroup fd
was being closed in the parent process before it forked the child. Then when
move_in_cgroup() is called for the child process, the file descriptor has
already been closed causing a failure for the second call to move_in_cgroup().
Moved the fd close after the fork call.

Change-Id: I6ae88b95c5410a7f56108e28eb3133f113e868d0
Signed-off-by: Garrison Bellack <gbellack@google.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>