Wipe device on policy error

If we fail to set a crypto policy on a system-DE directory, this is a
serious and unrecoverable condition; the only way forward is to erase
the entire device. In a future commit we will also allow users the
option of booting again.

Bug: 28318405
Change-Id: Iff1e52c5bbee1beed29dc4b609d24bfeb7d138da