cli: Modify configuration via CLI

cli: Modify configuration via CLI

In the past, only a few configuration parameters could be
modified via --test-params CLI argument and it was not easy
to find out their complete list.
This patch adds support for generic modification of any
configuration parameter via CLI argument --test-params
or by "Parameters" section of testcase definition.
Thus it is possible to customize a vsperf configuration
environment per testcase or for each vsperf execution.
Old CLI parameters duration, pkt_sizes, rfc2544_tests
and rfc2889_trials were renamed to TRAFFICGEN_DURATION,
TRAFFICGEN_PKT_SIZES, TRAFFICGEN_RFC2544_TESTS and
TRAFFICGEN_RFC2889_TRIALS to be consistent with
other configuration parameters.

JIRA: VSPERF-375

Change-Id: I50a1f4ff7250d754aa8af0295a9c7c1be8151175
Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: Bill Michalowski <bmichalo@redhat.com>
Reviewed-by: Antonio Fischetti <antonio.fischetti@intel.com>
Reviewed-by: <sridhar.rao@spirent.com>