fs_mgr: overlayfs: test: test mount -o rw,remount command

WAI: Using mount -o rw,remount command can only work after the
overlays are setup.  After the second 'adb disable-verity' or
'adb remount -R' has been issued; the first only disables
verity and does not setup the backing storage.  If mount remount
command is issued after the first on an overlayfs system, it will
report a r/o filesystem.

Add a test that confirms that at least this supported behavior is
working, we do not test the corner case.

In the case of overlayfs, we have declared we will not support the
mount remount operation until then; we would need to modify toybox
to add logic that resides inside adb remount service.  toybox is
allowed to be adjusted to compile under Android and bionic, but it
is not supposed to have code that is specific to Android.

Fix last test to before this one to move us back into this state.
Fix the adb_sh command parser to handle properly quoting arguments
as it passes them to adb, since we will need it working for this
added test.

Report the product serial number of build description to aid triage.

Test: adb-remount-test.sh
Bug: 109821005
Bug: 122602260
Bug: 123079041
Change-Id: Ida051dbe2a918182db97f0f22f64b299e3c0a068