Fixes and formatting to configure.py

* Fix a bug in error generation regarding true/false string parsing
* Some minor style fixes
diff --git a/configure.py b/configure.py
index d31ab27..05e3e80 100644
--- a/configure.py
+++ b/configure.py
@@ -327,19 +327,20 @@
   var = environ_cp.get(var_name)
   if var is not None:
     var_content = var.strip().lower()
-    if var_content in ('1', 't', 'true', 'y', 'yes'):
+    true_strings = ('1', 't', 'true', 'y', 'yes')
+    false_strings = ('0', 'f', 'false', 'n', 'no')
+    if var_content in true_strings:
       var = True
-    elif var_content in ('0', 'f', 'false', 'n', 'no'):
+    elif var_content in false_strings:
       var = False
     else:
-      raise UserInputError('Environment variable %s must be set as a boolean indicator.\n'
-                           'The following are accepted as TRUE : %s.\n'
-                           'The following are accepted as FALSE: %s.\n'
-                           'Current value is %s' %
-                           (var_name,
-                            ','.join(true_contents),
-                            ','.join(false_contents),
-                            var))
+      raise UserInputError(
+          'Environment variable %s must be set as a boolean indicator.\n'
+          'The following are accepted as TRUE : %s.\n'
+          'The following are accepted as FALSE: %s.\n'
+          'Current value is %s.' % (
+              var_name, ', '.join(true_strings), ', '.join(false_strings),
+              var))
 
   while var is None:
     user_input_origin = get_input(question)
@@ -627,8 +628,9 @@
 
   Raises:
     UserInputError: if a query has been attempted n_ask_attempts times without
-      success, assume that the user has made a scripting error, and will continue
-      to provide invalid input. Raise the error to avoid infinitely looping.
+      success, assume that the user has made a scripting error, and will
+      continue to provide invalid input. Raise the error to avoid infinitely
+      looping.
   """
   default = environ_cp.get(var_name) or var_default
   full_query = '%s [Default is %s]: ' % (
@@ -1121,16 +1123,15 @@
                               computecpp_toolkit_path)
 
 def set_trisycl_include_dir(environ_cp):
-  """Set TRISYCL_INCLUDE_DIR"""
-  ask_trisycl_include_dir = ('Please specify the location of the triSYCL '
-                             'include directory. (Use --config=sycl_trisycl '
-                             'when building with Bazel) '
-                             '[Default is %s]: '
-                             ) % (_DEFAULT_TRISYCL_INCLUDE_DIR)
+  """Set TRISYCL_INCLUDE_DIR."""
+  ask_trisycl_include_dir = (
+      'Please specify the location of the triSYCL include directory. (Use '
+      '--config=sycl_trisycl when building with Bazel) '
+      '[Default is %s]: ') % _DEFAULT_TRISYCL_INCLUDE_DIR
   while True:
     trisycl_include_dir = get_from_env_or_user_or_default(
-      environ_cp, 'TRISYCL_INCLUDE_DIR', ask_trisycl_include_dir,
-      _DEFAULT_TRISYCL_INCLUDE_DIR)
+        environ_cp, 'TRISYCL_INCLUDE_DIR', ask_trisycl_include_dir,
+        _DEFAULT_TRISYCL_INCLUDE_DIR)
     if os.path.exists(trisycl_include_dir):
       break