samples/crypto: Add mbedtls shim driver support

Normalizing variables names and make sure tag handling behavior, which
might be different among backends, does not make the test failing.

Also, improving debug logs in case of error.

Change-Id: Ic317948aab459bfa75c9a72ac48cb2d12a0d0706
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>