ftests: Add cgcreate systemd scope support

ftests: Add cgcreate systemd scope support

Add support for creating systemd scopes via the cgcreate command
line tool.

Python's subprocess.Popen.communicate() will not return until the
spawned process and all of its children finish running.  This will
cause a cgcreate of a scope to hang because libcgroup creates an
idle process in the newly-created scope.  Add a timeout to the run()
method so that it can complete even when a child process remains.

Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>
Reviewed-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>