RFR 8222275: sun/security/tools/keytool/Serial64.java: assertTrue: expected true, was false

[Weijun Wang]

Please take a review at

   https://cr.openjdk.java.net/~weijun/8222275/webrev.00/

Now the test would generate 10 to 30 certs. It could still fail, but the 
probably is extremely small now (2^-30 is 10^-9).

And the test would succeed early if a 64 bit SN is found. 

Thanks,
Max