6962419: TEST_BUG: java_io tests fails in samevm mode

[Alan Bateman]

This is another batch of updates to the regression tests to allow them 
be run in jtreg samevm mode. This batch covers the java.io tests. As 
expected, most of the issues are simply tests leaving files open, 
causing problems for subsequent tests running in the same VM. There are 
also several other random issues such as tests assuming the working 
directory, one test assuming it will be defined by the system class 
loader, and an issue cleaning up after a test that leaves a hidden file.

The webrev with the changes is here:
  http://cr.openjdk.java.net/~alanb/6962419/webrev/

With these changes (plus yesterday's batch to fix the serialization 
tests) then all 305 java.io tests pass, for me, in both samevm and 
othervm modes on all platforms.

Alan.