Extend line length of python files to 120 chars, to match C++

This will reduce the number of odd line breaks.

Bug: 156858180
Test: none (need to fix the linter to accept this for non-code)
Tag: #gd-refactor
Change-Id: Ibfd8282a7f41faf29665bba25c2c375420b693fa

.style.yapf

@@ -2,3 +2,4 @@
 # http://google.github.io/styleguide/pyguide.html
 based_on_style: google
 indent_width: 4
+column_limit: 120

system/gd/docs/architecture/style_guide.md

@@ -33,6 +33,7 @@ with the following modifications as shown in the
 ```yapf
 based_on_style: google
 indent_width: 4
+column_limit: 120
 ```
 
 ## Build files