1. Allow us to make the pass renderer fail during pillar rendering
when a secret corresponding with a pass path cannot be fetched.
For this we add a master config variable pass_strict_fetch.
2. Allow to have prefix for variables that should be processed
with the pass renderer.
For this we add a master config variable pass_variable_prefix.
3. Allow us to configure pass' GNUPGHOME and PASSWORD_STORE_DIR
environmental variables.
For this we add master config variables pass_gnupghome and pass_dir.
