bugfix: Fix evaluation order of parameters

bugfix: Fix evaluation order of parameters

This patch ensures, that testcase definition keywords vSwitch,
Trafficgen, VNF and Tunnel Type will have the highest priority
to override any values specified via ``Parameters`` section,
CLI arguments or configuration files.

JIRA: VSPERF-574

Change-Id: Ied799187d489325a32cc4854145fdf9901e7e3e2
Signed-off-by: Martin Klozik <martin.klozik@tieto.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>
Reviewed-by: Richard Elias <richard.elias@tieto.com>