buildhistory_analysis: Convert stream data (bytes) to strings
The bytes type variables are threat different as strings variables in python3,
so convert bytes to strings. This was found when using the
script buildhistory-diff, where the interpreter was yielding this error
TypeError: Type str doesn't support the buffer API
Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
