Blacklist the skypebuttons plugin

Even though plugins are disabled it happens that the libraries are
loaded and cause a crash since skypebuttons pulls Qt4 with it on
Linux and creates a dynamic linking error conflicting with Qt5
symbols.

Add the plugin library name to the blacklist to avoid it being
loaded altogether.
We have a similar fix in QtWebKit doing the same thing.

Change-Id: I6706d45d1f19252d3b60af7b97c0a3a729dfe8b7
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Remove the Running without renderer sandbox error message

We are currently not planing to enable the sandbox and the error
pollutes the auto tests output.

Change-Id: Idd2e7eeea8f890f55dd6b6d513a7a43890e7d5b4
Reviewed-by: Andras Becsi <andras.becsi@digia.com>