Also rename code uses from `project_name` to `oss_fuzz_project_name`, to
be more explicit, and use it to determine whether or not we're running
an OSS-Fuzz project or not.
For external fuzzing #6051.
1. Make coverage script accept an env var that controls where the generated report is written to. Use this in generate_coverage_report.
2. Rename CoverageGetter to OSSFuzzCoverage
3. Make affected_fuzz_targets get coverage object from clusterfuzz_deployment.
4. Add stubbed FilesystemCoverage class that will be used by non-OSS-Fuzz users.
5. Make ClusterFuzzLite able to return coverage object by downloading old coverage report and returning a FilesystemCoverage object.
6. Add stub to ClusterFuzzLite for uploading coverage.
Related: #6054
Also:
1. Support coverage builds.
2. Add an integration test for coverage builds and reports.
3. Refactor docker code so that there is less duplication in getting arguments for docker run, in particular when handling container (production) vs no container (testing).
4. Rename coverage.py to get_coverage_report.
5. Add tests for untested functions in docker.py
6. Add a test for get_fuzz_target_runner.
Abstract away OSS-Fuzz specific bits into the OSSFuzz implementation
of the ClusterFuzzDeployment class. This will make it easier to implement
support for other deployments of ClusterFuzz (including ClusterFuzzLite).
Oliver Chang