Support EmPy 4.x configuration API (#665)

There isn't a clean way to configure EmPy the way we need to which is
compatible with both EmPy 3.x and 4.x. Unfortunately, this means that
we'll need to have separate code paths.

Additionally, EmPy 4.x doesn't take the `name` argument to
Interpreter.string(). From what I can tell, it wasn't used for anything
interesting anyway. In particular, exception traces still contain
`<string>` instead of the file name.

colcon_core/shell/template/__init__.py

@@ -8,7 +8,6 @@
 from colcon_core.logging import colcon_logger
 try:
     from em import Interpreter
-    from em import OVERRIDE_OPT
 except ImportError as e:
     try:
         import em  # noqa: F401
@@ -35,13 +34,24 @@ def expand_template(template_path, destination_path, data):
     """
     output = StringIO()
     try:
-        # disable OVERRIDE_OPT to avoid saving / restoring stdout
-        interpreter = CachingInterpreter(
-            output=output, options={OVERRIDE_OPT: False})
+        try:
+            from em import Configuration
+        except ImportError:
+            from em import OVERRIDE_OPT
+            # disable OVERRIDE_OPT to avoid saving / restoring stdout
+            interpreter = CachingInterpreter(
+                output=output, options={OVERRIDE_OPT: False})
+        else:
+            interpreter = CachingInterpreter(
+                config=Configuration(
+                    defaultRoot=str(template_path),
+                    defaultStdout=output,
+                    useProxy=False),
+                dispatcher=False)
         try:
             with template_path.open('r') as h:
                 content = h.read()
-            interpreter.string(content, str(template_path), locals=data)
+            interpreter.string(content, locals=data)
             output = output.getvalue()
         finally:
             interpreter.shutdown()