RFR(xs): 8168796: relax vm options checking during CDS dump time

[Calvin Cheung]

bug: https://bugs.openjdk.java.net/browse/JDK-8168796

webrev: http://cr.openjdk.java.net/~ccheung/8168796/webrev.00/

Before this change, if any one of the following vm options 
("-module-path", "-add-modules", "--upgrade-module-path") is specified 
during CDS dump time, the vm exits with an error as follows:

bash-4.1$ java --upgrade-module-path=/tmp -Xshare:dump
Error occurred during initialization of VM
Cannot use the following option when dumping the shared archive: 
--upgrade-module-path

This change will print a warning message and continues as follows:

bash-4.1$ java --upgrade-module-path=/tmp -Xshare:dump
Warning: the --upgrade-module-path option is ignored when dumping the 
shared archive
Allocated shared space: 50577408 bytes at 0x0000000800000000
Loading classes to share ...

Test case is in the hotspot closed repo.

Testing:
     JPRT
     all tests under hotspot/test/runtime

thanks,
Calvin