host: Begin transforming host state serialization to use boltdb for persistence instead of flat files.

Signed-off-by: Eric Myhre <eric@flynn.io>
host: panic on errors persisting host state.

Signed-off-by: Eric Myhre <eric@flynn.io>
host: Replace restore process to match the converted persist process.  Factor persistence db initialization into separate method.  Switch backend restore interface to also take blob.

Signed-off-by: Eric Myhre <eric@flynn.io>
host: Only intialize persistence db once.

Signed-off-by: Eric Myhre <eric@flynn.io>