once it is lost, all data is gone.
Option '-B none' can by used to prevent backup. Option '-B path' can be
used to backup metadata to a different file than the default, which is
/var/backups/<prov>.eli.
The 'geli init' command also prints backup file location and gives short
procedure how to restore metadata.
The 'geli setkey' command now warns that even after passphrase change or keys
update there could be version of the master key encrypted with old
keys/passphrase in the backup file.
Add regression tests to verify that new functionality works as expected.
Update other regression tests so they don't create backup files.
Reviewed by: keramida, rink
Dedicated to: a friend who lost 400GB of his live by accidentally overwritting geli metadata
MFC after: 2 weeks
ba196edbd2