socket: disallow CBC cipher modes

This is related to CVE-2014-3566 a.k.a. POODLE.

	http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2014-3566

POODLE is specific to CBC cipher modes in SSLv3.  Because there is no
way to prevent SSLv3 fallback on a system with an unpatched version of
OpenSSL, users of such systems can only be protected by disallowing CBC
modes.  The default cipher-mode specification in our code has been
changed accordingly.  Users can still set their own cipher modes if they
wish.  To support them, the ssl-authz.t test script provides an example
of how to combine the CBC exclusion with other criteria in a script.

Change-Id: Ib1fa547082fbb7de9df94ffd182b1800d6e354e5
BUG: 1155328
Signed-off-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-on: http://review.gluster.org/8962
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>