IVGCVSW-7179 Segfault running ssd_mobilenet_v2_int8 with ExNet and delegate.

* model was declared in the TfLiteExecutor constructor, instead of intializing m_Model
* Working with this model that has 4 output we saw the the output names were not correct, this got fixed too 

Signed-off-by: Teresa Charlin <teresa.charlinreyes@arm.com>
Change-Id: I48f194ad4ba6af43d43e6eea336eb87ffee02dcc