Fix keytool availability detection
Fix keytool availability detection

No keytool version seems to recognize the -version option. All do seem
to have -help, although pre-JDK 1.7 ones return an error code with it,
but they're unsupported these days anyway so this should be good
enough.

dextero/Anjay,dextero/Anjay,dextero/Anjay,dextero/Anjay