fs_mgr: overlayfs: test: check for ext4 dedupe needing overlay

Check if any system partition looks like it has ext dedupe or
rather shared_blocks feature enabled, if so then we expect
overlayfs to kick in.  We do this to deal with any flakiness
in the test when right-sizing is not applied to the platform.

Minor: older devices mounted persist to /persist.

Test: adb-remount-test.sh
Bug: 109821005
Bug: 123079041
Change-Id: Iab7c6cf7f24f2c446aeb149e3f65d6793a42c6ea