RFR(m): 8150015: Integrate TraceTime with Unified Logging more seamlessly

[Robbin Ehn]

Hi, please review this enhancement.

This adds support for multiple UL tags in TraceTime.

Bug: https://bugs.openjdk.java.net/browse/JDK-8150015/
Webrev: http://cr.openjdk.java.net/~rehn/8150015/v1/webrev/

Tested with jprt hotspot and manually tested log output.

Thanks!

/Robbin