Related issue: #941

Description

This PR adds a command "topology-tags" to the HTTP API and the CLI interface to act exactly like the "topology" command but also to print the tags for each instance on the same line as the instance itself.

A proposal for the text formatting is specified in #941, but copied here:

$ orchestrator -c topology -i testhost:22293
testhost:22293     [unknown,unchecked,5.6.28-log,rw,STATEMENT,>>,P-GTID]
- testhost:22294   [unknown,unchecked,5.6.28-log,rw,STATEMENT,>>,P-GTID]
  - testhost:22295 [unknown,unchecked,5.6.28-log,rw,STATEMENT,>>,P-GTID]
- testhost:22296   [unknown,unchecked,5.6.28,rw,nobinlog,P-GTID]
- testhost:22297   [unknown,unchecked,5.6.28-log,rw,STATEMENT,>>,P-GTID]

$ orchestrator -c tag -i testhost:22293 -t in_service
$ orchestrator -c tag -i testhost:22293 -t role=backup

$ orchestrator -c tag -i testhost:22294 -t role=delayed

$ orchestrator -c tag -i testhost:22295 -t in_service

# The command which I am proposing, here I call it "topology-tags"
$ orchestrator -c topology-tags -i testhost:22295
testhost:22293     [unknown,unchecked,5.6.28-log,rw,STATEMENT,>>,P-GTID] [in_service,role=backup]
- testhost:22294   [unknown,unchecked,5.6.28-log,rw,STATEMENT,>>,P-GTID] [role=delayed]
  - testhost:22295 [unknown,unchecked,5.6.28-log,rw,STATEMENT,>>,P-GTID] [in_service]
- testhost:22296   [unknown,unchecked,5.6.28,rw,nobinlog,P-GTID] []
- testhost:22297   [unknown,unchecked,5.6.28-log,rw,STATEMENT,>>,P-GTID] []

I chose to add a separate command for this functionality instead of modifying "topology" or "topology-tabulated" in order to not modify existing APIs.

There is no option for printing tags for a tabulated topology, though this could be added if desired.

Testing

I added an integration test following the same pattern as the testing of the "topology" command, which invokes the orchestrator CLI to call the command which is added in this PR.

I did not see unit tests for the functions which I modified in go/inst/instance_topology.go so I did not add any. I also did not add any tests for the HTTP endpoint for the new command since I see only minimal testing in go/http/api_test.go, though I did run orchestrator in http mode and curled the new endpoint and invoked it with the modified orchestrator-client script from this PR.

In case this PR introduced Go code changes:

• contributed code is using same conventions as original code
• code is formatted via gofmt (please avoid goimports)
• code is built via ./build.sh
• code is tested via go test ./go/...