Rollup merge of #68947 - chrissimpkins:python-fmt, r=alexcrichton

Python script PEP8 style guide space formatting and minor Python source cleanup

This PR includes the following changes in the Python sources based on a flake8 3.7.9 (mccabe: 0.6.1, pycodestyle: 2.5.0, pyflakes: 2.1.1) CPython 3.7.6 on Darwin lint:

- PEP8 style guide spacing updates *without* line length changes
- removal of unused local variable assignments in context managers and exception handling
- removal of unused Python import statements
- removal of unnecessary semicolons

src/bootstrap/configure.py

@@ -393,11 +393,12 @@ for target in configured_targets:
 
 
 def is_number(value):
-  try:
-    float(value)
-    return True
-  except ValueError:
-    return False
+    try:
+        float(value)
+        return True
+    except ValueError:
+        return False
+
 
 # Here we walk through the constructed configuration we have from the parsed
 # command line arguments. We then apply each piece of configuration by