New storage dialogs.

Show a helpful dialog when a volume is unmounted or unmountable, or
when disk is unsupported.  Add both missing private volumes and
unsupported disks in the storage list.  Dialog to confirm when
forgetting private volume.

Finish volume detail activities when the volume becomes unmounted.

Show used space instead of free space to match string.  When init'ing
a volume on non-adoptable disk, just format as public.

Bug: 21737573, 21666225, 21737666, 21471429
Change-Id: Id60d5a398e2b7923ebebdc5cfaef33248d8d77bb