testcase: execution time

testcase: execution time

Measure the execution time for a testcase and add it to the log. We need
to report the test execution times for the testcases for OPNFV release
C. Modified the timing result in the csv + results file to display a
H:M:S format.

Change-Id: Ife9e361da5f8b3fc3721050ae3e6dce049f7402d
Signed-off-by: Maryam Tahhan <maryam.tahhan@intel.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>