github: Add continuous integration Github workflow

github: Add continuous integration Github workflow

Add a Github Actions continuous integration workflow.  This
workflow runs the unit tests, the cgroup v1 functional tests,
and the cgroup v2 functional tests.  The code coverage results
from all of the runs are collated at coveralls.io.

Like Travis CI, Github Actions currently does not provide a
distro that natively runs cgroup v2.  (And it also doesn't
expose the kernel boot command line.)  So, like our previous
Travis CI solution, unmount the cpuset controller and enable
it in cgroup v2.

Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>