RFR(S): 8168493: Convert TestBitMap_test to GTest

[Kirill Zhaldybin]

Dear all,

Could you please review this fix for 8168493?

WebRev: http://cr.openjdk.java.net/~kzhaldyb/webrevs/JDK-8168493/webrev.00/
CR: https://bugs.openjdk.java.net/browse/JDK-8168493

Changes:
1. Usual gtest conversion - asserts, file location etc
2. Simplified the test a bit - deleted unused template parameter, 
refactoring
3. Deleted friend class from BitMap class since we actually do not need it

Thank you.

Regards, Kirill