RFR(M): 8185436: jtreg: introduce keyword to disable cds tests

[Lindenmaier, Goetz]

Hi

we compile the VM without CDS support. Thus the CDS tests
fail. This change introduces a keyword 'cds' and marks 
the tests accordingly.
This change also fixes the keywords specified in gc/g1/TestSharedArchiveWithPreTouch.java.
There may only be one @key keyword in the test specification.
In runtime/CompressedOops/CompressedClassPointers.java only one test
case required CDS. I changed this sub case to succeed if CDS is not 
available.

Please review this change. I please need a sponsor.
http://cr.openjdk.java.net/~goetz/wr17/8185436-cdsKey/webrev.01/

Best regards,
  Goetz.