SoftwareCenterLauncherIcon: avoid the "Waiting to Install" tooltip to stay after installation
Be consistent with auto-hiding launcher.. Fixes: https://bugs.launchpad.net/bugs/925014, https://bugs.launchpad.net/bugs/1002440, https://bugs.launchpad.net/bugs/1012896. Approved by Marco Trevisan (Treviño), Brandon Schaefer, Thomi Richards.