Disallow installing over existing installation.
Disallow installing over existing installation.

Task-number: QTIFW-278

Change-Id: I5e435ac95c2efd699c1515592cdaaf698c3bc215
Reviewed-by: Karsten Heimrich <81d67632fe4bf9afb88a400b41aa25e19a1d2a12@digia.com>

olear/qtifw,olear/qtifw,olear/qtifw,olear/qtifw