Remove the use of PROTOCOL_SSLv3

The PROTOCOL_SSLv3 should not be used, as it can be exploited with
a protocol downgrade attack. Also, its support has been removed in
Debian, so it simply doesn't work at all now in Sid.

This patch removes PROTOCOL_SSLv3 from one of the possible protocols
used by oslo.messaging.

Closes-Bug: #1395095
Change-Id: I2c1977c3bfc1923bcb03744e909f2e70c7fdb14c
Merge "Remove the use of PROTOCOL_SSLv3"