Make Jaeger Agent url and Sampling parameters for traces configurable

Make the host:port of Jaeger Tracing agent configurable for each voltha component which is currently hard-coded in voltha-lib-go common pkg/log/utils.go file. Explore if component config should be used for same or should it be driven by Env variables.

Make Sampling scheme and other related parameters configurable. Also, explore if Remote controller Sampling will be appropriate for this client and how can it be achieved.