More lenient code coverage check

[ccaominh]

Description

Since there is not currently a good way to have fine-grain code coverage check exclusions, lower the coverage thresholds to make the check more lenient for now.

Also, display the code coverage report in the Travis CI logs to make it easier to understand how to improve coverage:

Diff coverage results:

  F = Function coverage
  L = Line coverage
  B = Branch coverage

------------------------------------------------------------------------------
org/apache/druid/cli/validate/DruidJsonValidator.java
------------------------------------------------------------------------------
254                       }
255                   );
256                 }
257               
258                 @Override
259                 public String toString()
260                 {
261 F | L             return "DruidJsonValidator{" +
262                          "logWriter=" + logWriter +
263                          ", jsonFile='" + jsonFile + '\'' +
264                          ", type='" + type + '\'' +
265                          ", resource='" + resource + '\'' +
266                          ", toLogger=" + toLogger +
267                          '}';
268                 }
------------------------------------------------------------------------------

Diff coverage statistics:
------------------------------------------------------------------------------
|     lines      |    branches    |   functions    |   path
------------------------------------------------------------------------------
|   0% (0/1)     | 100% (0/0)     |   0% (0/1)     | org/apache/druid/cli/validate/DruidJsonValidator.java
------------------------------------------------------------------------------
Total diff coverage:
 - lines: 0% (0/1)
 - branches: 100% (0/0)
 - functions: 0% (0/1)

ERROR: Insufficient line coverage of 0% (0/1). Required 50%.

---

This PR has:

• been self-reviewed.

[maytasm]

Do you think it's worth it to have separate threshold for each job? I am not sure what are the numbers currently on each job/module and if there's a wide range between jobs/modules or not.

[ccaominh]

Do you think it's worth it to have separate threshold for each job? I am not sure what are the numbers currently on each job/module and if there's a wide range between jobs/modules or not.

The thresholds are on the PR diff, so I think it should mostly be independent of the particular job/module.

[maytasm]

Do you think it's worth it to have separate threshold for each job? I am not sure what are the numbers currently on each job/module and if there's a wide range between jobs/modules or not.

The thresholds are on the PR diff, so I think it should mostly be independent of the particular job/module.

Thanks for clarification. LGTM!