Support importing codegen'd files in jinja templates

The resolver wasn't looking in the bazel-out/k8-opt/bin (or similar)
directory.

Change-Id: I762c62c691ab6efdc9afb55238e964d2475111a0
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/tools/build_rules/jinja2_generator.py b/tools/build_rules/jinja2_generator.py
index 3575e99..82222c3 100644
--- a/tools/build_rules/jinja2_generator.py
+++ b/tools/build_rules/jinja2_generator.py
@@ -19,11 +19,15 @@
         type=json.loads,
         help="Dictionary of parameters to replace in the template.")
     parser.add_argument("output", type=str, help="Output file to create.")
+    parser.add_argument(
+        "genfiles_dir",
+        type=str,
+        help="Directory where generated JSON files will be available.")
     args = parser.parse_args(sys.argv[1:])
 
     with open(args.template, 'r') as input_file:
-        template = jinja2.Environment(
-            loader=jinja2.FileSystemLoader(".")).from_string(input_file.read())
+        template = jinja2.Environment(loader=jinja2.FileSystemLoader(
+            [".", args.genfiles_dir])).from_string(input_file.read())
 
     output = template.render(args.replacements)
     with open(args.output, 'w') as config_file: