Avoid direct use of __cache__ in VumiMessage field test.
Avoid direct use of __cache__ in VumiMessage field test.

TouK/vumi,TouK/vumi,harrissoerja/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi