JDK 9 RFR of JDK-8075555:Add tiered testing definitions to the nashorn repo

[joe darcy]

Nashorn team,

Please review these changes to regularize Nashorn regression testing 
infrastructure with the JDK tiered testing policy. [1]

     JDK-8075555:Add tiered testing definitions to the nashorn repo
     http://cr.openjdk.java.net/~darcy/8075555.0/

In brief, testing tiers are defined (with an empty tier 1 for Nashorn) 
and an empty problem list is added.

When analogous changes are made in all the repositories, it will be 
possible to use a jtreg command like

     jtreg -exclude:ProblemList.txt [... other options...] :tier$N

for any repo.

Thanks,

-Joe

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