To perform sdk sandbox data isolation, the zygote gets the selinux label
of SDK sandbox storage (e.g. /data/misc_{ce,de}/<user-id>/sdksandbox)
before tmpfs is mounted onto /data/misc_{ce,de} (or other volumes). It
relabels it back once bind mounting of required sandbox data is done.
This change allows for the zygote to perform these operations.
Bug: 214241165
Test: atest SdkSandboxStorageHostTest
Change-Id: I28d1709ab4601f0fb1788435453ed19d023dc80b