Add functools.wraps on all function decorators

See [1], this enhances logging and keeps the docstrings.

[1]: https://docs.python.org/2/library/functools.html#functools.wraps

Change-Id: I33beb28abb9a1a955fb3b5a99fd5eec7efecbc06
Merge "Add functools.wraps on all function decorators"