RFR (S) 8221325: Add information about swap space to print_memory_info() on MacOS

[Schmelter, Ralf]

Hi,

please review this small change, which adds information about the swap space usage on MacOS to the output of print_memory_info(). This information was already present for other operating systems like Linux or AIX.

webrev: http://cr.openjdk.java.net/~rschmelter/webrevs/8221325/
bugreport: https://bugs.openjdk.java.net/browse/JDK-8221325

Best regards,
Ralf