sshd: fix proxy connections with the DefaultProxyDataFactory

sshd: fix proxy connections with the DefaultProxyDataFactory

The java.net.ProxySelector is quite a bit different from the one
in Eclipse. Eclipse (and the OS) uses "socks" as URI scheme to
look up a SOCKS proxy. java.net.ProxySelector needs "socket" as
scheme (and internally maps that to "socks" if and when it asks
the OS about the proxies).

Moreover, java.net.ProxySelector may return unresolved addresses,
whereas the Eclipse proxy selector always returns resolved addresses.

Fix both by explicitly resolving unresolved proxy addresses and using
scheme "socket" in the DefaultProxyDataFactory.

Tested manually with the jgit command-line tool using ssh -vvv -D7020
localhost and 3proxy as SOCKS5 proxies on localhost (3proxy with
user/password authentication). Start jgit with _JAVA_OPTIONS set to
"-DsocksProxyHost=<host> -DsocksProxyPort=<port>
-Djava.net.useSystemProxies=false" to test manually.

Bug: 548965
Change-Id: Ib81ae8255ac2f9c48268f172e7d8ebb4a792b66d
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>