Creating test data using 6-bit MSBF encoding doesn't work

There were no tests of encoding 

X-DFDL-US-ASCII-6-BIT-PACKED-MSB-FIRST

I added such a test, and it fails, not because the parser/unparser doesn't work,  but because the TDML runner doesn't create the data properly when using:

      <tdml:documentPart type="text" encoding="X-DFDL-US-ASCII-6-BIT-PACKED-MSB-FIRST">

test test_packed6BitMSBF fails because it uses the documentPart that doesn't work.

test test_packed6BitMSBF2 succeeds because it lays down the bits manually for the characters.