httpextbin: Add test case for repeatedly setting uri
httpextbin: Add test case for repeatedly setting uri

httpextbin stores uri which will be set a real source element
before paused state.

Change-Id: I8efee5b1a8ae0e72fe7594c1744ba52e1bf5a949
Reviewed-on: https://gpro.palm.com/29391
Reviewed-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>
Tested-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>

justinjoy/gst-plugins-lp,justinjoy/gst-plugins-lp