Executes the given command inside the environment and returns the output.

def _execute(self, args, log=True):
        """Executes the given command inside the environment and returns the output."""
        if not self._ready:
            self.open_or_create()
        output = ''
        error = ''
        try:
            proc = subprocess.Popen(args, cwd=self.path, env=self.env, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
            output, error = proc.communicate()
            returncode = proc.returncode
            if returncode:
                raise subprocess.CalledProcessError(returncode, proc, (output, error))
            return to_text(output)
        except OSError as e:
            # raise a more meaningful error with the program name
            prog = args[0]
            if prog[0] != os.sep:
                prog = os.path.join(self.path, prog)
            raise OSError('%s: %s' % (prog, six.u(str(e))))
        except subprocess.CalledProcessError as e:
            output, error = e.output
            e.output = output
            raise e
        finally:
            if log:
                try:
                    self._write_to_log(to_text(output))
                    self._write_to_error(to_text(error))
                except NameError:
                    pass