RFR: 6402201: ProcessAttachTest.sh needs better synchronization

[Erik Gahlin]

Could I have a review of this test fix.

It appears it takes more than 10 s to write to a file on slow machines. 
Instead of sleeping 10 s the test now polls for the file to appear. 
There may be other issues with the test, but it's hard to know without 
ruling this race out.

Thanks
Erik

Testing:
- I have run the test 20+ times locally on a highly saturated CPU 
without failure
- JPRT.

Bug:
https://bugs.openjdk.java.net/browse/JDK-6402201

Webrev:
http://cr.openjdk.java.net/~egahlin/6402201_1/