Test duration, recommend libraries, retry session, manual test import...

• Adjust manual test case import from nitrate [#319]
• Move the test convert deps into a separate package
• Support importing manual test cases from Nitrate
• Merge the non-zero exit codes for linting errors
• Fix several test export issues [fix #337]
• Adjust distro checks, remove the dry parameter
• Generalized Guest.details() [fix #310]
• Adjust the test coverage for tmt plan/test lint
• Update documentation with virtualization tips
• Make sure the duration timer is always canceled
• Merge the new retry_session functionality [#328]
• Exit with non-zero code if linting fails
• Merge fix for the double fmf extension [#327]
• Prevent koji from trying to build packages on i686
• Retry requests in case of network failure
• Avoid double fmf extension when creating plans and stories
• Improve the maximum test duration handling
• Remove vagrant from tmt-all recommended packages
• Detect beakerlib libraries from recommend as well
• Simplify packit custom create archive command
• Make the httpd test example a bit more interesting
• Append dots to fix tmt run --help message summary
• Document multiple configs and extending steps