Show errors explicitly

[turicas]

• If you run sbc ssh to a remote machine that does not have sbc installed, it should show an error
• [Fixed] If you run sbc some_plugin on remote machine and for some reason sbc can't execute the command locally (invalid SSH key, connection lost, plugin does not exist etc.), it should show an error message
• [Fixed] Redirect 2 greps to /dev/null
• Verify if localhost is running a SSH daemon before connecting (sbc ssh)