Do not canonicalize overlay config test paths

Some devices may not have certain partitions available and the
OverlayConfigTests use hardcoded paths to test OverlayConfig
functionality. This change ensures that the temporary directory
created to test OverlayConfig has all of the partitions defined in
PackagePartitions#SYSTEM_PARTITIONS within it.

Bug: 187020117
Bug: 187020675
Test: atest OverlayConfigTest
Change-Id: I511e24b7ccfe82e6e89ceea7107457439793ef77