Add pre-commit robot-framework tidy

Add pre-commit robot-framework tidy

Use pre-commit to handle robot tidy tool rather than maintaining our
own. This tool is handy because it will automatically correct the
local files on "git commit" after pre-commit is installed for the
first time.

Install pre-commit using tox with `tox -e pre-commit`.

Change-Id: I64d802b2d0754160755bce3e50272a5f28af4d72
Signed-off-by: Thanh Ha <zxiiro@gmail.com>