vts_fs_test: Only check /data and /metadata for rw partitions.

Some rw /proc/mounts entries are FUSE.

Also, add some diagnostics for failures.

Bug: 318962836
Test: vts_fs_test on Pixel
Change-Id: I85dec8b37f1a061b1eca597aba3887b598b699f5
1 file changed