Further progress on allowing synchronous metrics requests.
Further progress on allowing synchronous metrics requests.

Tests are still needed and asynchronous requests still need work.

jbonnet/son-gkeeper,sonata-nfv/son-gkeeper,sonata-nfv/son-gkeeper,felipevicens/son-gkeeper,jbonnet/son-gkeeper,dang03/son-gkeeper,sonata-nfv/son-gkeeper,felipevicens/son-gkeeper,sonata-nfv/son-gkeeper,jbonnet/son-gkeeper,felipevicens/son-gkeeper,dang03/son-gkeeper,dang03/son-gkeeper,felipevicens/son-gkeeper,dang03/son-gkeeper,jbonnet/son-gkeeper