Android Settings Page: Disable avd settings if no sdk is configured

Task-number: QTCREATORBUG-10719
Change-Id: Icba278610119a204b19b0422bfa778d9a2c71d86
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
TargetSetupPage: Fix crash for multiple calls to initializePage

The first fix didn't take into account that m_baseLayout might change
after the constructor. Ensure that the widgets now are always owned
by the right layout and only the right layout.

Task-number: QTCREATORBUG-10643
Change-Id: I5c9f9fd6a98c16490eafaf84eda090c13f19ed15
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>