RFR: 8195649: reorganize tests for java.util.Optional

[Stuart Marks]

Hi all,

Please review this changeset, which reorganizes (basically rewrites) the tests 
for Optional and Optional{Double,Int,Long}. The new arrangement clusters all the 
assertions together into check* methods. These are then called on the results of 
the various factories and other monadic operations. This reduced the amount of 
test code and actually increased the test coverage slightly.

Bug:

	https://bugs.openjdk.java.net/browse/JDK-8195649

Webrev:

	http://cr.openjdk.java.net/~smarks/reviews/8195649/webrev.0/

Thanks,

s'marks