Fixes:
```
70run-post-tasks: invoking /var/cache/cosmos/model/post-tasks.d/018packages
Your configuration specifies to merge with the ref 'refs/heads/master'
from the remote, but no such ref was fetched.
```
Before staging a puppet module for install the latest git tag is
verified using the available gpg key identities. The git tag pattern
can be overriden using a fourth argument in cosmos-modules.conf.