Create misc_ce and misc_de mirror storage

Create a mirror directory for misc_ce and misc_de storage by bind
mounting the respective directories. This is done for the defaul null
volume only, and other volumes are handled at a later staged.

When an SDK sandbox process is spawned and data isolation needs to
occur, the sdksandbox directories present in the misc directories will
be used to bind mount from, after tmpfs is mounted on the original.

Bug: 214241165
Test: atest GtsSdkSandboxInprocessTests
Ignore-AOSP-First: Will cherry pick based on other CLs in the topic

Change-Id: Icb1dc7d7fbd53a5c3853acf2f9d4d75b278d7295
Merged-In: Icb1dc7d7fbd53a5c3853acf2f9d4d75b278d7295