build: add ability to disable some plugins from packaging and tests

When custom-packaging the VPP artifacts, it can be useful to exclude
some of the core plugins from packaging/testing, for some reasons.
A removal of a plugin(s) from the worktree needs to be tracked as
a separate change, and thus is tricky from the maintenance
point of view.

This change adds the ability to "pretend they do not exist" -
plugins which are added to the comma-separated environment
variable "VPP_EXCLUDED_PLUGINS" will not be added to the build
process and not packaged.

The tests do not have the 1:1 relationship as plugins,
so they might need to be modified separately. This change
includes some of these modifications as an example.

Type: feature
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
Change-Id: Id31562d00a01ced1acbb4996a633517cbd6f09d8

test/test_abf.py

@@ -3,6 +3,8 @@
 from socket import inet_pton, inet_ntop, AF_INET, AF_INET6
 import unittest
 
+from config import config
+
 from framework import VppTestCase, VppTestRunner
 from vpp_ip import DpoProto
 from vpp_ip_route import (
@@ -119,6 +121,11 @@ class VppAbfAttach(VppObject):
         return "abf-attach-%d-%d" % (self.policy_id, self.sw_if_index)
 
 
+@unittest.skipIf(
+    "acl" in config.excluded_plugins,
+    "Exclude ABF plugin tests due to absence of ACL plugin",
+)
+@unittest.skipIf("abf" in config.excluded_plugins, "Exclude ABF plugin tests")
 class TestAbf(VppTestCase):
     """ABF Test Case"""