Persist error d-bus objects

Use Cereal to implement serialization and de-serialization of
properties of error d-bus objects.

Serialize and persist error d-bus objects as they are put on the bus.
De-serialize and restore them (if persistent ones exist) when
phosphor-log-manager starts up.

Change-Id: I1f5df1abbe74bfdb86e3e82a78ff7115e90e2112
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
8 files changed