teststeps: Improvements and bugfixing of teststeps

teststeps: Improvements and bugfixing of teststeps

This patch introduces several improvements and small bugfixes
of teststeps. These changes were identified during implementation
of OVS/DPDK regression tests.

Patch content:
* teststeps: step aliases were implemented
* teststeps: improved filtering by regex for any step, which returns string
  or list of stings; filter will process all lines
* teststeps: support for log object
* teststeps: support for trafficgen get_results call
* teststeps: configurable suppression of step validation
* trafficgen: remove old results before traffic is executed
* trafficgen: support for flow control on/off (IxNet)
* trafficgen: support for configurable learning frames (IxNet)
* trafficgen: support for runtime changes of TRAFFICGEN_PKT_SIZES, _DURATION
  and _LOSSRATE
* vnf: flush pexpect output of previous commands
* vnf: use execute_and_wait() to ensure correct cmds order
* vnf: dpdk vHost User interface name set according to its type,
  e.g. dpdkvhostuserclient
* vswitch: support for OVS restart
* decap: simplify configuration of tunneling decapsulation tests
* settings: values of all configuration options are restored after TC execution
* modified formatting of test description used by --list
* testcase name and description is logged before its execution
* small bugfixes

JIRA: VSPERF-539

Change-Id: I550ba0d897ece89abd3f33d6d66f545c4d863e7b
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: Sridhar Rao <sridhar.rao@spirent.com>
Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>