Create the checkin subdirectory under misc_ce

We need some storage on the device to backup the token for checkin
services. So users won't lose the checkin tokens when they clear
the app's storage. If the device accidentally loses the
token without backup, it won't be able to checkin again until
factory reset.

Because we want the token to be user specific, put it under misc_ce
and let vold create the sub-directory.

Bug: 197636740
Test: boot device, check selinux label of the dir
Change-Id: I0e19dcb7f4feb98fd9d1013cfd84b56ff1325373