cg: use one path style throughout cg restore code

This commit is in preparation for the (hopefully last :) restore special cpuset
patch.

Previously, we installed the cgroup service fd after calling
prepare_cgroup_dirs, which meant that we had to carry around the temporary
directory name in order to put things in the right place. The
restore_cgroup_prop function uses the cg service fd instead of carrying around
the full path. This means that we can't sue restore_cgroup_prop, without first
sanitizing the path. Instead, we install the service fd before calling
prepare_cgroup_dirs, and all the code just references that instead of carrying
around the temporary path.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/util.h

@@ -212,7 +212,7 @@ static inline bool strstartswith(const char *str, const char *sub)
 /*
  * mkdir -p
  */
-int mkdirp(const char *path);
+int mkdirpat(int fd, const char *path);
 
 /*
  * Tests whether a path is a prefix of another path. This is different than