initial python service classifier basic implementation

Change-Id: I835d43604a1e16a5ed190222df591d5a30a6393a
Signed-off-by: Jim Guichard <jguichar@cisco.com>
imported nsh_encode and removed build_packet from service_classifier
added parameters into build_packet()

Change-Id: Ib26795461d7ef6ee7b8829d1c00170dc5fa2e51c
Signed-off-by: Jim Guichard <jguichar@cisco.com>