Created by: luotao1

A implement of https://github.com/PaddlePaddle/Paddle/issues/10028#issuecomment-383112371

The result of make test ARGS='-R tensorrt_convert_test -V':

76: [==========] Running 1 test from 1 test case.
76: [----------] Global test environment set-up.
76: [----------] 1 test from tensorrt
76: [ RUN      ] tensorrt.ConvertBlock
76: I0423 13:14:39.315845 17146 convert.cc:42] convert a fluid mul op to tensorrt fc layer without bias
76: I0423 13:14:39.315907 17146 convert.cc:42] convert a fluid Conv2d op to tensorrt conv layer without bias
76: [       OK ] tensorrt.ConvertBlock (0 ms)
76: [----------] 1 test from tensorrt (0 ms total)
76: 
76: [----------] Global test environment tear-down
76: [==========] 1 test from 1 test case ran. (1 ms total)
76: [  PASSED  ] 1 test.
1/1 Test #76: tensorrt_convert_test ............   Passed    5.66 sec

Will add TensorRTEngine as a member variable of TensorRTConverter class after #10003.