Add new required variant linux-64-required-duroff to evergreen.yml

In order to ensure that new tests are correctly tagged, there are currently 3 build variants which execute burn_in_tests in a distinct configuration, using the expansion macro ${burn_in_tests_build_variant}:

• enterprise-rhel-62-64-bit-required-majority-read-concern-off
• enterprise-rhel-62-64-bit-required-inmem
• rhel-62-64-bit-required-mobile

To catch tests requiring the requires_journaling tag, we can add another build variant, linux-64-required-duroff, in evergreen.yml, similar to enterprise-rhel-62-64-bit-required-majority-read-concern-off.