Fix converting double to MojDecimal

:Release Notes:
Fixed issue with rounding during conversion from double to MojDecimal

:Detailed Notes:
Fixed tests DecimalTest.ctor_double_with_rounding and
DecimalTest.floatValue_reconvert which were broken because of missing
rounding in conversiong from double.

:Testing Performed:
test_core and gtest_mojocore

:QA Notes:

:Issues Addressed:
[GF-36958] MojDecimal in DB8 have issues with rounding and exponent

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>

Change-Id: I46147bca3ae3fd46b5dcbdc7df5fe8b9625e3375
Reviewed-on: https://g2g.palm.com/3306
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Roger Stringer <roger.stringer@lge.com>