Code review request: 8014196: ktab creates a file with zero kt_vno

[Weijun Wang]

Hi Valerie

Please take a look at
   http://cr.openjdk.java.net/~weijun/8014196/webrev.01/

KeyTab.getInstance() used to return null if the keytab file does not 
exists, but since we supported dynamic ktab, the result is never null. 
But the KeyTab object has not initialize its kt_vno.

The fix includes two parts:

1. Initialize kt_vno in KeyTab even if isMissing or !isValid

2. Make clear in what cases ktab.exe should fail.

Thanks
Max