currently tox env for code coverage does not measure anything
as it tries to measure the coverage of 'ironic-staging-drivers' package,
while the actual package name is 'ironic_staging_drivers'.
- erases current coverage data first
- fixes project name expected by 'coverage'
- adds coverage reporting in the end of 'tox -ecover' run
- omits tests file from both coverage and report
- adds 'cover' to .gitignore (auto-generated as part of coverage report)