RFR(s): 8152182: Possible overflow in initialzation of _rescan_task_size and _marking_task_size

[sangheon]

Hi all,

Please review this change for CMSRescanMultiple and CMSConcMarkMultiple 
flags.

Both flags are set by "CardTableModRefBS::card_size_in_words * 
BitsPerWord * flag" which potentially would make an overflow with their 
maximum value without setting range. And these flags also would make an 
arithmetic overflow when calculating with the size and the start address 
of reserved area. In addition, CMSRescanMultiple needs an alignment check.

CR: https://bugs.openjdk.java.net/browse/JDK-8152182
Webrev: http://cr.openjdk.java.net/~sangheki/8152182/webrev.00
Testing: JPRT, runtime/commandline JTREG for all platforms

Thanks,
Sangheon