Update unit tests to provide consistent directory map

[jphickey]

Is your feature request related to a problem? Please describe.
The "file-api-test" and "osal_loader_UT" unit tests rely on a real FS_BASED directory map that is provided by the BSP. This creates an undesired dependency on the BSP volume table in these test cases, in that they must provide a map for /cf.

Describe the solution you'd like
Test should be BSP-agnostic. A map for the directory used by the test case can be provided locally as part of this test setup. A relative system directory can be used (e.g. "./test") to make this platform-agnostic.

Additional context
This will allow to run unit tests without a BSP-provided volume table.

Requester Info
Joseph Hickey, Vantage Systems, Inc.