The keystore password should be a .txt file containing a plain text password for the keystore. If you do not specify a keystore and password one will be generated for you. You will find a debug.keystore and debug.keystore.pass.txt in the project root. The generated keystore will use the default password android (ie same as used by the official Android build tools).
More info here: https://defold.com/manuals/android/#creating-an-android-application-bundle