libcutils: update fs_config tests for current behavior

Update fs_config tests for the new behavior in
a8eb0072.

Before the above CL, fs_config_cmp() would match any partition prefix
to any path, even if there is not a logical relationship between them.
For example, these two lines in the test the demonstrate the changed
behavior:

{ true,  "vendor/lib",             "system/vendor/lib/hw",    true },
{ true,  "system/vendor/lib",      "vendor/lib/hw",           true },

The first line should match and does; it is testing that files located
at system/vendor/lib/hw are matched by an fs_path_config entry
specified as vendor/lib.  This is to allow for applying the policy we
have for the vendor partition to files in /system/vendor in the case
that there is no vendor partition.

The second line should not match.  This is testing that a file
that's located at vendor/lib/hw is matched by an fs_path_config entry
specified as system/vendor/lib.  This is backwards; we do not want to
have policy specified for system/vendor to impact policy for the
vendor partition.

Also, we never have any relationships from /system/oem to /oem or
/system/odm to /odm, so these are logically unrelated and should fail
to match.  We do however have a relationship from /vendor/odm to /odm,
so this test is added.

Test: libcutils unit tests pass on CF
Change-Id: I026f0233e00bbd0aad9bc0fb701aef000d2a037c