RFR: JDK-8177763: Getting an hprof dump via jcmd could benefit from stronger option checking

[Gary Adams]

Thee are several reported problems using jcmd for obtaining heap dumps.

Some users are confused by the positional argument for a filename
when a similar jfr command uses "key=value" syntax.

Some users are confused by the basic nature of the command, where the jvm
executing the heap dump is running in a different current directory than
the jcmd itself.

This is a proposed fix to report the current directory and the filename
when the heap dump is successfully written or if an error occurs. There
is also a proposed fix to handle the case when the user provided
"key=value" inputs. If the key matches the argument name, then the
user intended the value to be used.

   Issue: https://bugs.openjdk.java.net/browse/JDK-8177763
   Webrev: http://cr.openjdk.java.net/~gadams/8177763/webrev.00/