merge RHEL8 changes
- add rhel8 specific installation part in renamed devsetup to envsetup
- remove dependency installation from yaml as difficult to run those in rhel7/8/fedoras
- remove macsec for rhel8
- install pppoe-server to run ppp tests in rhel8
- make symlinks checks better to reflect changes in rhel8
- give more time to rhel8 tshark tests (due to bug1578940)