android build: make building testnet apk easier

Just uncomment line 53 in make_apk, and you get a testnet apk that can co-exist with your mainnet install.
No need to do a clean rebuild of ".buildozer/" either.

contrib/android/make_apk

@@ -44,8 +44,13 @@ info "apk building phase starts."
 
 # Uncomment and change below to set a custom android package id,
 # e.g. to allow simultaneous mainnet and testnet installs of the apk.
+# defaults:
 #   export APP_PACKAGE_NAME=Electrum
 #   export APP_PACKAGE_DOMAIN=org.electrum
+# FIXME: changing "APP_PACKAGE_NAME" seems to require a clean rebuild of ".buildozer/",
+#        to avoid that, maybe change "APP_PACKAGE_DOMAIN" instead.
+# So, in particular, to build a testnet apk, simply uncomment:
+#export APP_PACKAGE_DOMAIN=org.electrum.testnet
 
 if [ ! $CI ]; then
     # override log level specified in buildozer.spec to "debug":

run_electrum

@@ -330,6 +330,9 @@ def main():
             'gui': android_gui,
             'single_password':True,
         }
+        if util.get_android_package_name() == "org.electrum.testnet.electrum":
+            # ~hack for easier testnet builds. pkgname subject to change.
+            config_options['testnet'] = True
     else:
         config_options = args.__dict__
         f = lambda key: config_options[key] is not None and key not in config_variables.get(args.cmd, {}).keys()