Revisit the use of ObjectMessage on pinger and avail-creator

Due HAWKULAR-459 the behaviour of ObjectMessage has been changed.

ObjectMessage is being used in pinger/avail-creator as a way to send data to alerts component using the bus in an indirect way.

Per discussion in:

https://github.com/hawkular/hawkular-bus/commit/9b3f067554345230e78b112bc52a4f617e7bc15f#commitcomment-12242141

We are going to review the use of ObjectMessage in hawkular/modules.