docs: Enhancement of IxNetwork configuration guide

docs: Enhancement of IxNetwork configuration guide

Configuration guide has been updated with description of
IxNetwork specific configuration options. New section was added
with description of test results sharing between IxNetwork and
VSPERF.
Additional changes:
* wrong formatting inside installation.rst was fixed
* description of IxNetwork configuration was updated inside ixnet.py

JIRA: VSPERF-302

Change-Id: Ida0e086e69b82fd1f9821d16ea750b2dec1d5aa2
Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Maryam Tahhan <maryam.tahhan@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: <bmichalo@redhat.com>