[backport] Disabled SI-6987.

It causes spurious failures - a typical example:

[partest] testing: [...]/files/run/t6987.scala                                  [FAILED]
[partest] did not get the string expected, full results were:
[partest] Fast Scala compiler version 2.11.0-20130126-111937-f01e001c77 -- Copyright 2002-2013, LAMP/EPFL
[partest] [Given arguments: -shutdown -verbose]
[partest] [Transformed arguments: -shutdown -verbose -current-dir /localhome/jenkins/b/workspace/scala-checkin-manual]
[partest] [VM arguments: ]
[partest] java.net.ConnectException: Connection refused
[partest] [Connecting to compilation daemon at port 32808 failed; re-trying...]
[partest] [No compilation server running.]
[partest]
(cherry picked from commit 53d5df5c1d52b941732c243159de4f44456f03b4)