CLOUDIFY-2370 fix constant reference
CLOUDIFY-2370 added logging and fixed typo
CLOUDIFY-2370 use virtualenv as ds_file path
CLOUDIFY-2370 fix flake
CLOUDIFY-2370 swtich celery common dependency to develop
Merge pull request #2 from CloudifySource/feature/CLOUDIFY-2370-plugins-as-python-libs

Feature/cloudify 2370 plugins as python libs