Merge lp://qastaging/~kissiel/checkbox/fix-mem-inflation into lp://qastaging/checkbox

This MR fixes mem problem in Checkbox-Converged

CommandOutput page used a buffer that was filled with the strings that job's command printed and periodically timer synced that output onto the text area. As the buffer qml's "property string" was used. This somehow broke garbage collecting and the strings were never freed from memory. By changing the type to 'property var' fixed all problems.

Why?

I don't know.

Here: http://paste.ubuntu.com/12310269/ is the code I did to pinpoint where/how the problem may be solved. If you want to reproduce the bug, in the pastebinned code change the type of bufferedIO from 'var' to 'string'.