Add version 2.0.21 to align with stx 3.0:
- Add the recipe for version 2.0.21
- Set the preferred version to 2.0.21
- Enable build with openssl10
- Add patch libevent-ipv6-client-socket.patch from
libevent-2.0.21-4.el7.tis.2.src.rpm
Story: 2008204
Task: 40988
Change-Id: Ic0d24eb39b01d0a8d3092d2241ab4f2ad13b605e
Signed-off-by: Jackie Huang <jackie.huang@windriver.com>