I had installed java and used alternatives to create a symbolic link. When I tried to create an Apollo instance, I got the same error message as you. Apparently the Apollo install expects keytool to be available in your search path.
I added a symbolic link for keytool, removed the previous aborted instance, and then the Apollo instance creation completed successfully.
In my case, the alternatives command was:
sudo alternatives --install /usr/bin/keytool keytool /opt/jre1.8.0_51/bin/keytool 1
This assumes you want to put the link in /usr/bin. And of course the second path argument needs to match where you've put the Java install.