jinja2: Don't hardcode utf-8 encoding for imported files

UTF-8 encoding for template imports was hardcoded from the beginning -
from 320f29b2 (Add jinja2 "import" directive support.)

Since in the previous patch we added option for input/output encoding,
it makes sense to also use it, instead of hardcoding utf-8.

/reviewed-by @vpelletier  (on nexedi/slapos.recipe.template!1)

slapos/recipe/template/jinja2_template.py

@@ -92,9 +92,10 @@ class RecipeBaseLoader(BaseLoader):
     """
     Base class for import classes altering import path.
     """
-    def __init__(self, path, delimiter):
+    def __init__(self, path, delimiter, encoding):
         self.base = os.path.normpath(path)
         self.delimiter = delimiter
+        self.encoding = encoding
 
     def get_source(self, environment, template):
         path = self._getPath(template)
@@ -103,7 +104,7 @@ class RecipeBaseLoader(BaseLoader):
             raise TemplateNotFound(template)
         mtime = os.path.getmtime(path)
         with file(path) as f:
-            source = f.read().decode('utf-8')
+            source = f.read().decode(self.encoding)
         return source, path, lambda: mtime == os.path.getmtime(path)
 
     def _getPath(self, template):
@@ -171,7 +172,7 @@ class Recipe(object):
                 expression_type]
             import_dict[alias] = loader_type(
                 expression_handler(expression, buildout, name, options),
-                import_delimiter,
+                import_delimiter, self.encoding,
             )
         if import_dict:
             loader = RelaxedPrefixLoader(import_dict,