service: add unit tests

service: add unit tests

Add a bunch of unit tests, to ensure that the service
core functions are operating as expected.

As part of these tests a dummy service is registered which
allows identifying if a service callback has been invoked
by using the CPU tick counter. This allows identifying if
functions to start and stop service lcores are actually having
effect.

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>