JDK 9 RFR of JDK-8075546: Add tiered testing definitions to the langtools repo

[joe darcy]

Hello,

As part of implementing the tiered testing policy in JDK 9 [1], please 
review the changes for

     8075546: Add tiered testing definitions to the langtools repo
     http://cr.openjdk.java.net/~darcy/8075546.0/

A few comments, I've made the TEST.ROOT file in langtools consistent 
with the keywords and minimum jtreg version used in the jdk repo.

The one javadoc test GetTask_DocletClassTest.java uses randomness and 
I've marked it accordingly.

I've created an empty problem list file so that command lines to invoke 
the test suites for a repository can be more uniform across repositories.

Thanks,

-Joe

[1] http://mail.openjdk.java.net/pipermail/jdk9-dev/2015-March/001991.html