RFR: 8240532: heap inspection prints trailing @ after name of module without version

[Stefan Karlsson]

Hi all,

Please review this patch to remove a trailing @ after module names of 
modules without a version.

https://cr.openjdk.java.net/~stefank/8240532/webrev.01/
https://bugs.openjdk.java.net/browse/JDK-8240532

The heap inspection functionality generates and prints a class histogram.

Full image builds show module name and version as 'name at version':
[3,640s][trace][gc,classhisto      ] GC(1)    4: 5067         162144  
java.lang.String (java.base at 15-internal)

Exploded builds don't have a version and prints 'name@'
[4,361s][trace][gc,classhisto      ] GC(1)    3: 7144         228608  
java.lang.String (java.base@)

This looks weird and I propose that we drop the trailing @ when there's 
no version string:
[4,361s][trace][gc,classhisto      ] GC(1)    3: 7144         228608  
java.lang.String (java.base)

This affects the output of:
* -Xlog:classhisto*=trace
* jcmd <pid> GC.class_histogram
* inspectheap attach operation
* jmap -histo

I've run the tests I could find that were using these operations. Other 
than that I intend to run tier1-3.

Do others agree with this change?

Thanks,
StefanK