Multiple bugfixes for NFVbench

Multiple bugfixes for NFVbench

[NFVBENCH-52] NFVbench should ignore the port security settings if not
available
[NFVBENCH-53] NFVbench should support to use software mode for TRex
[NFVBENCH-54] NFVbench container should also map kernel sources when
available to build KOs
[NFVBENCH-55] Documentation enhancements to have better examples for
using "$PWD"
[NFVBENCH-57] NFVbench should support to build kernel modules on redhat
distros

Change-Id: Id6792d6711393b07ca59396c276a026bec9f1e86
Signed-off-by: Yichen Wang <yicwang@cisco.com>