Use test policy engine configuration file.

The test device may have configurable engine configuration file.
However, the test only load default engine. In that case, the test
should not use the configurable engine configuration file. Or it will
fail the test.

Bug: 360937480
Test: atest audiopolicy_tests
Flag: EXEMPT bugfix
Change-Id: Id3a553b2c4a2ea50e22fcff0f4163b7741c6713b