jpkg enhancements to create signed modules

[Vincent Ryan]

Hello,

Please review these code changes to support the creation of signed modules:

  http://cr.openjdk.java.net/~vinnie/6951048/webrev.00/webrev/

It adds the following new options to the jpkg tool:

  -S, --signer  <ID>         : module signer's identifier
  -k, --keystore <location>  : module signer's keystore location
  -t, --storetype <type>     : module signer's keystore type
  --nosign                   : do not sign the module
  --nopassword               : do not prompt for a keystore password

Appropriate default values are supported and keystore passwords may be
supplied to jpkg by redirecting standard input.


This is just one of a number of changes to support signed modules throughout
jigsaw.

Please send me your comments as I'm hoping to address any issues and integrate
these changes by the end of this week.

Thanks.