tests: decrpoxy: deploy decproxy at decodebin
tests: decrpoxy: deploy decproxy at decodebin

Change-Id: I56e3f45322f92887b5c4ca0bdfc6675272499586
Reviewed-on: https://gpro.palm.com/60911
Reviewed-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>
Tested-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>

justinjoy/gst-plugins-cool,justinjoy/gst-plugins-cool