remote/config: allow use of environment variables in exporter config

This extends the jinja2 templating support in exporter configuration file with
support for using OS environment variables.

Signed-off-by: Esben Haabendal <esben@geanix.com>
[r.czerwinski@pengutronix.de: rebased]
Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>

CHANGES.rst

@@ -65,6 +65,8 @@ New Features in 0.3.0
   Labgrid.
 - ``labgrid-client write-image`` gained a new argument ``--mode`` to specify
   which tool should be used to write the image (either ``dd`` or ``bmaptool``)
+- Exporter configuration file ``exporter.yaml`` now allows use of environment
+  variables.
 
 Breaking changes in 0.3.0
 ~~~~~~~~~~~~~~~~~~~~~~~~~

doc/configuration.rst

@@ -2211,3 +2211,7 @@ Use ``#`` for line statements (like the for loops in the example) and ``##``
 for line comments.
 Statements like ``{{ 4000 + idx }}`` are expanded based on variables in the
 Jinja2 template.
+
+The template processing also supports use of OS environment variables, using
+something like `{{ env['FOOBAR'] }}` to insert the content of environment
+variable `FOOBAR`.

labgrid/remote/config.py

@@ -2,6 +2,7 @@
 
 import attr
 import jinja2
+import os
 
 from ..util.yaml import load
 from ..exceptions import NoConfigFoundError
@@ -23,7 +24,7 @@ def __attrs_post_init__(self):
             raise NoConfigFoundError(
                 "{} could not be found".format(self.filename)
             )
-        rendered = template.render()
+        rendered = template.render(env=os.environ)
         pprint(('rendered', rendered))
         self.data = load(rendered)
         pprint(('loaded', self.data))