Execute a command and get the output of the finished process.

def getOutput(self, command, env={}, path=None,
                  uid=None, gid=None, usePTY=0, childFDs=None):
        """Execute a command and get the output of the finished process.
        """
        deferred = defer.Deferred()
        processProtocol = _SummaryProcessProtocol(deferred)
        self.execute(processProtocol, command, env,
                     path, uid, gid, usePTY, childFDs)
        @deferred.addCallback
        def getStdOut(tuple_):
            stdout, _stderr, _returnCode = tuple_
            return stdout
        return deferred