Android: Rework Create AVD dialog

Filter the list of api levels to only show those that can be created.

Change-Id: I7aaaa58324ca44176e39982cda29d746011fa346
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
QtVersions: Hide error message from addQtVersion mkspec parse

We only do this parse to decide which factory to use for this qt version.
The mkspec will be parsed again by the qtversion anyway. That parse will
output any errors in the mkspec.

Change-Id: I6587e2ddbc92c8ee23e1ea4ad3942e7e19585e0d
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>