if command prompt doesn't open
I'm not sure, but it would be happen( in my environment, winxp japanese, xubuntu works fine), especially if file path contains " "white space or some char sequences, actually, which should be properly escaped.
for that case, sadly my installer cannot help, please double click and run the uploading script by yourself.
appcfg.cmd, if mac
appcfg.sh is the script file. those files locate in the following child directory.
appengine-java-sdk-1.8.9 ↳ bin ↳ appcfg.cmd, appcfg.sh