force:source:deploy --coverageformatters cobertura | Incorrect class filename in Cobertura XML reports

### Summary

When running force:source:deploy with --coverageformatters cobertura, it generate a cobertura xml file with the coverage results. However the filename path is invalid which means ci/cd tooling can't associate the coverage with the actual file.

### Steps To Reproduce:
Just run a source:deploy with test level set as RunLocalTest or RunSpecifiedTests and make sure coverageformatters is set as cobertura.
```shell
sfdx force:source:deploy -g -w 999 --testlevel RunSpecifiedTests -p force-app/main/default/classes/SampleClass.cls -r "SampleClass_Test" --junit --resultsdir tests --coverageformatters cobertura --checkonly --verbose
```
### Expected result

Cobertura xml with valid filename should be generated.
```xml

.

```

### Actual result
Filename path is completely incorrect
```xml

.

```

### System Information

- Which shell/terminal are you using? bash

- If you are using `sfdx`
**sfdx-cli/7.168.0 darwin-x64 node-v14.15.4**