pkt_gen: STC - RFC 2889 Address Learning and Caching Support

pkt_gen: STC - RFC 2889 Address Learning and Caching Support

This patch adds RFC-2889 address-learning-rate test and
address-caching-capacity tests. The patch includes following changes

1. 01_testcases.conf: testcase definitions are added for new tests
2. results_constants.py: 3 new results constants are added, removed
   unsupported constants
3. testcenter-rfc2889-rest.py: Added support to these two new
   tests. Removed un-necessary synchronization of db-file. 5 new
   configuration parameters are added - which are explained in (4).
4. trafficgen.rst: Configuration description for rfc2889 tests are
   added. Stale information is removed.
5. testcenter.py: Support for two new tests are added. Separate
   functions for results analysis and parameter settings are added.
6. traffic_controller_rfc2889.py: Calls to functions in testcenter.py,
   based on the traffic_type, are added.

Removed trailing whitespaces from trafficgen.rst

JIRA: VSPERF-395

Change-Id: Ie6ca87519b7736e7410d7f0e60904579934af24a
Signed-off-by: Sridhar K. N. Rao <sridhar.rao@spirent.com>