Fix a bug with handling of binary data

When checking the length of the data in a request, Barbican assumes
that data is UTF-8 encoded strings.  Barbican then attempts to
decode all data from UTF-8 to byte strings, which results in an
exception when the data does not conform to UTF-8.

Change-Id: Iea41cdc3c7fe518302202921f6637571c351b932