FS functional test - add calls to get default mount point and extension for each file type

[skliper]

Is your feature request related to a problem? Please describe.
Functional test just calls with UNKNOWN, should exercise each type (although response verification isn't necessary since it's implementation defined and "helper" functions are really best effort).

cFE/modules/cfe_testcase/src/fs_util_test.c

Lines 36 to 42 in eb9c523

	void TestFileCategory(void)
	{
	UtPrintf("Testing: CFE_FS_GetDefaultMountPoint, CFE_FS_GetDefaultExtension");
	UtAssert_NULL(CFE_FS_GetDefaultMountPoint(CFE_FS_FileCategory_UNKNOWN));
	UtAssert_NULL(CFE_FS_GetDefaultExtension(CFE_FS_FileCategory_UNKNOWN));
	}

Describe the solution you'd like
Exercise each defined file type

Describe alternatives you've considered
None

Additional context
None

Requester Info
Jacob Hageman - NASA/GSFC