common.testCase: fix find_sdk_tools when aapt is installed in /usr/bin
common.testCase: fix find_sdk_tools when aapt is installed in /usr/bin

The testlogic was broken when having both aapt in /usr/bin and also as
part of the android sdk.

fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver