Remove rendundant parentheses of cfg help strings

There is a hacking review https://review.openstack.org/#/c/74493/.
That makes me be aware we maybe have rendunant parentheses.
We'd better clean the parentheses, Python will handle that well.

Change-Id: I275aaa49450d8088d93b3e19138850c359a4abae
Merge "Remove rendundant parentheses of cfg help strings"