RFR: JDK-8223464: Improve version string for Oracle CI builds

[Erik Joelsson]

This change changes how the version string will look in Oracle CI 
builds. A string that current looks like this:

13-internal+0-jdk13-jdk.844

Will instead look like this:

13-ea+0-844

For projects, the $PRE string will be used to identify the project, like 
this:

13-panama+0-844

While in the area, I also moved the setting of "ea" or not in the $PRE 
string to a property in the version-numbers file.

Note that these changes only affect builds produced by Oracle.

Bug: https://bugs.openjdk.java.net/browse/JDK-8223464

Webrev: http://cr.openjdk.java.net/~erikj/8223464/webrev.01/

/Erik