Support query service instance registered in the registry via emctl

[zhao-kun]

emctl should provide subcommand to query service instance, the output looks like:

SERVICE                      TENANT        INSTANCE                                            CANARY           STATUS 
-------------------------------------------------------------------------------------------------------------
vets-service        spring-petclinic   vets-service-79b955b989-22b4q          lv1                     ON_LINE
vets-service        spring-petclinic   vets-service-79b955b989-42b4q                                    ON_LINE
vets-service        spring-petclinic   vets-service-79b955b989-32b4g                                    OUT_OF_SERVICE

When users query service instance, they can specify a (or many) condition(s) to filter result, conditions:

1. service name, filter by services' name.
2. tenant, filter by tenant name.
3. canary, filter by canary version.
4. status, filter by service instance status.