HttpURLConnectionDownloaderService: don't include a stack trace for SocketTimeoutException

[php-coder]

2020-04-20 12:24:18.946 [user:2 ] DEBUG 14682 --- [qtp188523822-5081] w.f.s.HttpURLConnectionDownloaderService : Couldn't download file: connect() has failed

java.net.SocketTimeoutException: connect timed out
        at java.net.PlainSocketImpl.socketConnect(Native Method) ~[na:1.8.0_151]
        at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) ~[na:1.8.0_151]
        at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) ~[na:1.8.0_151]
        at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) ~[na:1.8.0_151]
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_151]
        at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_151]
...

As this this a common case, we don't need a stack trace, just a message is enough.