pep8, ignore W606 'async' and 'await' are reserved keywords starting with Python 3.7

This error exists in pyjs extension, but pyjs isn't going to Python3.
'noqa' isn't working for W606, so this warning is disabled completely.
'async' and 'await' are still checked by pylint.

          <xsd:attribute name="Command" type="xsd:string" use="optional" default="make -C %(buildpath)s all BEREMIZSRC=%(src)s BEREMIZCFLAGS=%(cflags)s MD5=%(md5)s USE_BEREMIZ=1 FROM_BEREMIZ=1"/>