testpmd: Simplify GUEST's testpmd configuration

testpmd: Simplify GUEST's testpmd configuration

Testpmd has a lot of parameters and vsperf was able
to modify only a few of them through dedicated GUEST's
specific configuration options. Old configuration
options were replaced by one generic GUEST_TESTPMD_PARAMS,
which allows to modify any of existing testpmd parameters.
Detection of testpmd execution was changed to be independent
on TXQ flags setting.
Documentation was modified to reflect GUEST_TESTPMD change.
Also doc formatting was fixed at several places.

JIRA: VSPERF-380

Change-Id: Ie0bf290320f3b22ef6be6b55ed553235bbcb4aff
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: Bill Michalowski <bmichalo@redhat.com>
Reviewed-by: Antonio Fischetti <antonio.fischetti@intel.com>