Make the decoder Cfg available to encoder tests..

Adds decoder config as a changeable parameter to unit tests, and
changes end to end test to use commonly used parameters to enable
base test of tiles encoding and frame parallel decoding.

Change-Id: I5d23a6857303b4d68b92b15c3f2f04a1bcb4c2bb

test/encode_test_driver.h

@@ -238,6 +238,7 @@ class EncoderTest {
 
   bool                 abort_;
   vpx_codec_enc_cfg_t  cfg_;
+  vpx_codec_dec_cfg_t  dec_cfg_;
   unsigned int         passes_;
   unsigned long        deadline_;
   TwopassStatsStore    stats_;