RFR(S) 8241004: NMT tests fail on unalinged thread size with debug build

[boris]

Hi,

Please review the following change.

http://cr.openjdk.java.net/~bulasevich/8241004/webrev.00
http://bugs.openjdk.java.net/browse/JDK-8241004

The stack size created by the implementation of the pthread library is 
not necessarily page aligned. It is weird, but it is not forbidden: the 
pthread library may add some gap on it own. My change removes stack size 
alignment assert checks and tunes NMT committed range calculation for 
the case of unaligned stack size.

thanks,
Boris