Add helper methods to nova.paths

We only ever do one of two things with the global path options:

  1) Reference the option in the default of another option so that the
     value can be interpolated it

  2) Use the value of the option to build a path

Add helper methods for both these cases - e.g. basedir_def() for the
former case and basedir_rel() for the latter case. This makes it much
more obvious how and where these options are used.

Change-Id: I7fd94a329fe911761d02d94e5381e950c6668d56

nova/paths.py

@@ -36,3 +36,33 @@ path_opts = [
 
 CONF = cfg.CONF
 CONF.register_opts(path_opts)
+
+
+def basedir_def(*args):
+    """Return an uninterpolated path relative to $pybasedir."""
+    return os.path.join('$pybasedir', *args)
+
+
+def bindir_def(*args):
+    """Return an uninterpolated path relative to $bindir."""
+    return os.path.join('$bindir', *args)
+
+
+def state_path_def(*args):
+    """Return an uninterpolated path relative to $state_path."""
+    return os.path.join('$state_path', *args)
+
+
+def basedir_rel(*args):
+    """Return a path relative to $pybasedir."""
+    return os.path.join(CONF.pybasedir, *args)
+
+
+def bindir_rel(*args):
+    """Return a path relative to $bindir."""
+    return os.path.join(CONF.bindir, *args)
+
+
+def state_path_rel(*args):
+    """Return a path relative to $state_path."""
+    return os.path.join(CONF.state_path, *args)