adb: better error messages on deduplicated filesystems.

If BOARD_EXT4_SHARE_DUP_BLOCKS is true, "adb remount" will error saying
the filesystem is read-only. Instead, it will now list affected
partitions and explain why they can't be remounted.

Bug: 64109868
Test: adb remount with deduplicated system image
Change-Id: Ida737a6be8e9fe9ea26300897d82b1a149e72f6d