[style] apply google python style guide (#4501)

This commit applies and enforces Google's python style for tests.

script/bootstrap

@@ -56,6 +56,10 @@ install_packages_apt()
 
     # add clang-format for pretty
     sudo apt-get -y install clang-format-6.0
+
+    # add yapf for pretty
+    python3 -m pip install yapf || echo 'Failed to install python code formatter yapf. Install it manually if you need.'
+    
 }
 
 install_packages_opkg()
@@ -89,6 +93,9 @@ install_packages_brew()
         brew install llvm@6
         sudo ln -s "$(brew --prefix llvm@6)/bin/clang-format" /usr/local/bin/clang-format-6.0
     }
+
+    # add yapf for pretty
+    python3 -m pip install yapf || echo 'Failed to install python code formatter yapf. Install it manually if you need.'
 }
 
 install_packages_source()

script/make-pretty

@@ -53,6 +53,7 @@ main()
 {
     trap at_exit INT TERM EXIT
     make_pretty
+    python3 -m yapf --style google -ipr "${SRC_DIR}/tests" "${SRC_DIR}/tools"
 }
 
 main "$@"

script/pystyle.cfg

@@ -1,16 +0,0 @@
-[flake8]
-# it's not a bug that we aren't using all of hacking, ignore:
-# E203: White space before ':' (see #python#black#315).
-# W503: Line break occurred before a binary operator (see #python#black#README.md).
-ignore = E203, W503
-
-# relax the length limitation for now.
-max-line-length = 119
-max-doc-length = 119
-
-# Print the source code generating the error/warning in question.
-show_source = True
-show-source = True
-
-# print the total number of errors.
-count = True