[VOL-5010] - Clone unit tests to run on a v2.12 branch

docs/release/README.md
makefiles/release/help.mk
-------------------------
  o Temp release documentation until text can be o-fficially
    added in the howto:release section of docs.voltha.org.

Makefile
makefiles/include.mk
makefiles/release/include.mk
makefiles/release/required.mk
makefiles/release/targets.mk
-----------------------------
  o Add makefile infra used to create and clone master tests for release.
  o Logic is conditional, makefile library will only load when named
    targets are requested.
  o make help and make help-voltha-release document new targets.
  o create-jobs-release-nightly is simply a placeholder for now.
    - Nightly unit tests are still bundled in the mega voltha job config.
    - Still need to isolate and separate these out so tests can be
      anchored for branch driven release testing.

Change-Id: I692166e17c5e04d87d112f317b9fead1d5c4090d
diff --git a/makefiles/include.mk b/makefiles/include.mk
index be08b19..d4fb1e3 100644
--- a/makefiles/include.mk
+++ b/makefiles/include.mk
@@ -35,6 +35,8 @@
 include $(ONF_MAKE)/git-submodules.mk
 include $(ONF_MAKE)/gerrit/include.mk
 
+include $(ONF_MAKE)/release/include.mk
+
 include $(ONF_MAKE)/todo.mk
 include $(ONF_MAKE)/help/variables.mk