Fix db re-use in DatabaseSuite in gtest_db_core

:Release Notes:
Fixed false-negative for DatabaseSuite.dump_and_load.

:Detailed Notes:
DatabaseSuite.dump_and_load and JsonSuite.paser_loaddefault used same
folder for their test database. When dump_and_load started later than
parser_loaddefault it read data from previous test.

:Testing Performed:
gtest_db_core

:QA Notes:

:Issues Addressed:
[GF-30407] Unit tests failing: test_db_core and gtest_db_core

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

Change-Id: Ia33585ec54c1839b51721d57b96299bd33407c4a
Reviewed-on: https://g2g.palm.com/3245
Reviewed-by: Build Verification
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Maksym Sditanov <maxim.sditanov@lge.com>
Tested-by: Maksym Sditanov <maxim.sditanov@lge.com>
Reviewed-by: Roger Stringer <roger.stringer@lge.com>