Fix for ambiguous and broken disk formatting dialog

This patch ensures that the path-string from StorageNotification is converted
to the appropriate StorageVolume so that it can be correctly passed to the
formatting class. It also displays this path to the user so that it is clear
what will be deleted.

While trying to use a USB flash drive over OTG, the drive's FS somehow got
corrupted, so Android gave me a notification to re-format it. Okay, so then
a dialog pops up that doesn't specify what volume/device it will format, and
I incorrectly assumed it would be the USb drive. However this activity defaults
to the main internal memory for some reason, and wiped my data. Thank God for
them internets... (Dropbox)

Change-Id: I5621dff3cfd12a173b0d793398cf729333f97263