Return full prefix path of environment defined by `name`.

def get_prefix_envname(self, name, log=False):
        """Return full prefix path of environment defined by `name`."""
        prefix = None
        if name == 'root':
            prefix = self.ROOT_PREFIX

#        envs, error = self.get_envs().communicate()
        envs = self.get_envs()
        for p in envs:
            if basename(p) == name:
                prefix = p

        return prefix