Disable flaky presentation compiler test.

Francois is investigating the root cause as part of his
work on stabilizing Scaladoc preview in the IDE.

The test seems to only fail on the windows nightly build.
I suspect this is due to a slower or loaded machine.
Disable tests for SI-7020

These are still impudently being non-deterministic.

I've reopened the ticket so we can take another swing at it.
A well targetted s/HashMap/LinkedHashMap/ will almost certainly
be the salve.

	fail - neg/t7020.scala  [output differs]% scalac t7020.scala
	t7020.scala:3: warning: match may not be exhaustive.
	It would fail on the following inputs: List((x: Int forSome x not in (1, 2, 4, 5, 6, 7))), List((x: Int forSome x not in (1, 2, 4, 5, 6, 7)), _), List(1, _), List(2, _), List(4, _), List(5, _), List(6, _), List(7, _), List(??, _), List(_, _)
	 List(5) match {
	     ^
	t7020.scala:10: warning: match may not be exhaustive.
	It would fail on the following inputs: List((x: Int forSome x not in (1, 2, 4, 5, 6, 7))), List((x: Int forSome x not in (1, 2, 4, 5, 6, 7)), _), List(1, _), List(2, _), List(4, _), List(5, _), List(6, _), List(7, _), List(??, _), List(_, _)
	 List(5) match {
	     ^
Merge pull request #3043 from retronym/topic/flaky

Disable flaky tests