Poor exception handling in client.rb

[claudijd]

Ran into this once, but it wasn't reproducible on the same client after the first attempt.

/Users/jclaudius/code/ssh_scan/lib/ssh_scan/client.rb:72:in `read': Connection reset by peer (Errno::ECONNRESET)
    from /Users/jclaudius/code/ssh_scan/lib/ssh_scan/client.rb:72:in `get_kex_result'
    from /Users/jclaudius/code/ssh_scan/lib/ssh_scan/scan_engine.rb:42:in `scan_target'
    from /Users/jclaudius/code/ssh_scan/lib/ssh_scan/scan_engine.rb:119:in `block (2 levels) in scan'

We should consider trapping this exception so it doesn't cause the scan to hard fail, but still report it. We might also consider at some point to retry some actions if they fail or cause an exception to increase our chances of success.