RFR(s): 8067187: -XX:MaxMetaspaceSize=20m -Xshare:dump caused JVM to crash

[Calvin Cheung]

JBS: https://bugs.openjdk.java.net/browse/JDK-8067187

This fix is to add a check on the MaxMetaspaceSize when performing CDS 
archive dumping.

With the fix, instead of a crash, it will print and error message like 
the following and exit:

Java HotSpot(TM) 64-Bit Server VM warning:
The MaxMetaspaceSize of 20971520 bytes is not large enough.
Either don't specify the -XX:MaxMetaspaceSize=<size>
or increase the size to at least 33554432.

Tested manually via command line and jtreg test on the new test.

webrev: http://cr.openjdk.java.net/~ccheung/8067187/webrev/

thanks,
Calvin