pkg/schema: Add a test for mixedArrayFromString().
pkg/schema: Add a test for mixedArrayFromString().

As per review comments/feedback.

Change-Id: I6db67214b8aa613f0e07914e7ba784820abcbfb1

toshnix/camlistore,toshnix/camlistore,toshnix/camlistore,toshnix/camlistore,toshnix/camlistore,toshnix/camlistore,toshnix/camlistore,toshnix/camlistore,toshnix/camlistore