common: always set android ndk env vars
common: always set android ndk env vars

Also, add the ndk to PATH at the beginning, in case any other ndks are
already in it.

Fixes #176.

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