Defaults to stdout in play2-tail

Running 'tail' for a play2 project without parameters does not default to stdout like intended. Instead, It prints:

        error: <class 'xml.parsers.expat.ExpatError'>, not well-formed (invalid token): line 6, column 1: file: /usr/lib/python2.7/xmlrpclib.py line: 557
        Fatal error: sudo() received nonzero return code 2 while executing!

This commit fixes that and does not change the behaviour when an argument is provided.