RFR: 8146879: Truncate new UL log files

[Marcus Larsson]

Hi,

Please review the following patch to make sure UL truncates existing log 
files before writing to them. Since files are opened in append mode, 
truncation isn't done automatically, so instead the patch adds an 
attempt to remove the log file before opening it.

Webrev:
http://cr.openjdk.java.net/~mlarsson/8146879/webrev.00/

Issue:
https://bugs.openjdk.java.net/browse/JDK-8146879

Testing:
Included test through JPRT

Thanks,
Marcus