Source nvm before using it

According to https://github.com/creationix/nvm#install-script,
we should, you know, actually source the script rather than just cloning
the repo and then ignoring it.

Change-Id: I046af8d38cf7288fcb3fac74cd6839d4e006ca90

roles/upload-npm/tasks/main.yaml

@@ -16,6 +16,8 @@
   shell:
     executable: /bin/bash
     cmd: |
+      export NVM_DIR="$HOME/.nvm"
+      [ -s "$NVM_DIR/nvm.sh" ] && . "$NVM_DIR/nvm.sh" # This loads nvm
       nvm install node
       nvm use node
       npm publish --ignore-scripts {{ zuul.executor.work_root }}/artifacts/{{ zuul.project.short_name }}-{{ project_ver }}.tar.gz