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_acl_plugin.py

@@ -5,6 +5,7 @@
 import unittest
 import random
 
+from config import config
 from scapy.packet import Raw
 from scapy.layers.l2 import Ether
 from scapy.layers.inet import IP, TCP, UDP, ICMP
@@ -20,6 +21,7 @@ from vpp_acl import AclRule, VppAcl, VppAclInterface, VppEtypeWhitelist
 from vpp_ip import INVALID_INDEX
 
 
+@unittest.skipIf("acl" in config.excluded_plugins, "Exclude ACL plugin tests")
 @tag_fixme_vpp_workers
 class TestACLplugin(VppTestCase):
     """ACL plugin Test Case"""