PuppetDB backend: allow to override URL scheme in config

* In some environments the PuppetDB hosts might listen only on HTTP on
  localhost and the Cumin host might connect to it via an SSH tunnel.
* Allow to override the default HTTPS scheme of the PuppetDB URL in the
  configuration.

Bug: T218441
Change-Id: I14ecd78cf2652fb11eb471f8597c57db1321cb98

cumin/backends/puppetdb.py

@@ -135,7 +135,7 @@ class PuppetDBQuery(BaseQuery):
       ``host10[10-42].*.domain or (not F:key1 = value1 and host10*) or (F:key2 > value2 and F:key3 ~ '^value[0-9]+')``
     """
 
-    base_url_template = 'https://{host}:{port}'
+    base_url_template = '{scheme}://{host}:{port}'
     """:py:class:`str`: string template in the :py:meth:`str.format` style used to generate the base URL of the
     PuppetDB server."""
 
@@ -162,6 +162,7 @@ def __init__(self, config):
         self._endpoint = None
         puppetdb_config = self.config.get('puppetdb', {})
         base_url = self.base_url_template.format(
+            scheme=puppetdb_config.get('scheme', 'https'),
             host=puppetdb_config.get('host', 'localhost'),
             port=puppetdb_config.get('port', 443))
 

doc/examples/config.yaml

@@ -16,6 +16,9 @@ environment:
 puppetdb:
     host: puppetdb.local
     port: 443
+    # [optional[ Allow to override the default HTTPS scheme with HTTP in case the connection to PuppetDB is secured in
+    # other ways (e.g. SSH tunnel)
+    scheme: https
     api_version: 4  # Supported versions are v3 and v4. If not specified, v4 will be used.
     urllib3_disable_warnings:  # List of Python urllib3 exceptions to ignore
         - SubjectAltNameWarning