RFR: JDK-8027963: Create unlimited policy jars.

[Erik Joelsson]

Here is the next part of fixing things for the JCE team. With this 
patch, the build will always build both the limited and unlimited set of 
policy jars, just like the old build did. In an OPENJDK build, the 
configure option --enable-unlimited-crypto will still be used to choose 
which one gets installed in jdk/lib and the resulting images.

The directory structure for the unsigned and signed security jars in the 
build directory have also changed according to the suggestion in the bug:

     jdk/
         jce/
             unsigned
                 jce.jar...
                 policy
                     limited
                         local_policy.jar...
                     unlimited
                         local_policy.jar...
             signed
                 jce.jar...
                 policy
                     limited
                         local_policy.jar...
                     unlimited
                         local_policy.jar...

Finally, the README.txt is copied to the unlimited directory for 
OracleJDK builds.

Webrev: http://cr.openjdk.java.net/~erikj/8027963/webrev.01/
Bug: https://bugs.openjdk.java.net/browse/JDK-8027963

/Erik