new dependency: hunter in entity-manager

[Patrick Venture]

A new dependency was added:
 https://github.com/openbmc/entity-manager/blob/master/CMakeLists.txt#L8

My builds are failing because they don't have access to the internet
and this repository is downloaded outside the scope of bitbake (so it
isn't getting cached).

Also, I find the possibility of it going away troubling:
https://github.com/ruslo/hunter/issues/1921

James, is there a hunter bitbake recipe? I didn't see one, but with a
name that generic as a noun, it's possible I just missed it.

Is it only required for unit-tests?  If so, can you fix the cmakelist
to only add it for that build?  If unit-tests are always set to build,
can we add a flag to disable them when built for bitbake?  we do that
for other repos?

Patrick