[NEXUS-7659] Disable all SSL (including SSLv3) protocols by default

https://issues.sonatype.org/browse/NEXUS-7659
http://bamboo.s/browse/NX-OSSF390

Similar to changes done in http client 4.3.6 SSLConnectionSocketFactory
This is in sync with what we exclude as protocols in https://issues.sonatype.org/browse/NEXUS-7595 (all SSL protocols)
The approach here is taken from http client 4.3.6 from the same class we used as base for NexusSSLConnectionSocketFactory.