Only enable verbose gc log for -Xlog levels trace, debug, info

[pshipton]

Levels off, warning, error do not enable the verbose gc log

Issue #13865

[pshipton]

jenkins compile alinux64 jdk11

[pshipton]

Successful build https://openj9-jenkins.osuosl.org/job/Build_JDK11_aarch64_linux_Personal/147/

The -Xlog tests are passing https://openj9-jenkins.osuosl.org/view/Test/job/Grinder/348/

[pshipton]

jenkins compile zlinux,win jdk11

[pshipton]

This does not fix #13865

https://openj9-jenkins.osuosl.org/view/Test/job/Grinder/346

[keithc-ca]

https://www.eclipse.org/openj9/docs/xlog/ doesn't mention any legal suffixes for -Xlog:gc, and I couldn't find any documentation for other implementations that would suggest we should consider off, or any of the levels recognized by this change. Please provide some more context so I can understand the motivation here.

[pshipton]

See "Available log levels" at https://docs.oracle.com/en/java/javase/11/tools/java.html#GUID-BE93ABDC-999C-4CB5-A88B-1994AAAC74D5
Only one level can be specified, and with the exception of off, the level includes all the lower levels. i.e. setting warning also enables error, etc.
This PR is based on my judgment call that the error and warning levels should not enable the OpenJ9 verbose gc log.

[pshipton]

jenkins compile alinux64 jdk11

[pshipton]

Tests still passing https://openj9-jenkins.osuosl.org/view/Test/job/Grinder/355