On the remote host, use an installed virtualenv executable (e.g. the
        globally installed virtualenv on the path) to create a virutal
        environment.  The venv directory MUST NOT already exist.

def create(self):
        '''
        On the remote host, use an installed virtualenv executable (e.g. the
        globally installed virtualenv on the path) to create a virutal
        environment.  The venv directory MUST NOT already exist.
        '''
        # require that the venv does not yet exist.
        if self.exists():
            raise Exception('Path already exists. Abort creation. venv={}'.format(self.venv))

        # create the venv dir
        run('mkdir -p {}'.format(self.venv))

        # create the virtual environment
        run('{virtualenv} {venv}'.format(virtualenv=self.virtualenv, venv=self.venv))