(#21427) Deprecate YAML over the network

Issue a deprecation warning whenever YAML is encoded or decoded in the
http handler.
(#21427) Submit reports in PSON format

This changes the agent to submit reports in PSON. An effect of this
change is that reports will not be able to submit to masters that do not
have the changes for CVE-2013-3567 which allow the master to parse
PSON formatted reports.