[SDFAB-1197] First stab to update ONOS to py3

Update has been performed only on the scripts and the
executables strictly necessary for the following use cases:

- Build (including Intellij)
- Tests (including Intellij)
- Docker build (including dev and yourkit)
- Upload snapshot (including local)
- Release

Finally, fix the ability to run ONOS using onos-local targets,
stc and docker stc (aka up4 stc env). Last but not least, updated
the azul image to a newer one which exports also the PYTHONENCODING

Change-Id: Ie96f3a9c76dbba83b1fc3896a372f1045d3d7ccc
diff --git a/tools/build/onos-release-prerequisites b/tools/build/onos-release-prerequisites
index 92e201d..c1605ac 100755
--- a/tools/build/onos-release-prerequisites
+++ b/tools/build/onos-release-prerequisites
@@ -50,7 +50,7 @@
 
 # Tests availability of the required tools
 function testToolchain {
-    for tool in bash python git java javac mvn tar; do
+    for tool in bash python3 git java javac mvn tar; do
         testTool $tool;
     done
     testGerritTool