NEXUS-6838: "Rude" fix, adding SNI to TLS/HTTPS

This is the "rude" way as described in HTTPCLIENT-1119.

Other solution is described in other comment, in short: create
"plain" socket, and then wrap that socket with SSLSocket, but
for that to work you'd need to have host dedicated SSLContext
(for each HOST you access).

SNI works only on Java7+
Export sun.security.ssl from the system bundle so nexus-core can import it (also clean up the extra packages with newlines)
Merge pull request #717 from sonatype/NEXUS-6838-https-sni

REVIEW NEXUS-6838: "Rude" fix, adding SNI to TLS/HTTPS