Skip vm image tests on Travis

Also support Python 3.9

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

.travis.yml

@@ -13,9 +13,10 @@ python:
   - "3.6"
   - "3.7"
   - "3.8"
+  - "3.9"
 
 # Scripts to run at install stage
 install: ./configure --dev
 
 # Scripts to run at script stage
-script: tmp/bin/pytest
+script: tmp/bin/pytest --ignore=tests/test_vmimage.py