Need to handle INFO_OUTPUT_BUFFERS_CHANGED in an encode test

MSDK OMX plugin will reconfiged the output buffers when the first encode
frame coming up. After that, Output buffers will be re-allocated and a
message MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED will be raised simultaneously,
up-layer application have to handle this message and get the new
outputbuffers, otherwise it will be wrong.

But the cts test EncodeVirtualDisplayWithCompositionTest did not handle
the message MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED cause the outputbuffers
are outdated, then crash happened when java want to read them.

Modified the test case to handle MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED as
EncoderTest.java does.

Change-Id: I32ea59a9d34880e33d374d1999990596b865f8ea
Singed-off-by: Ying Chang <ying.chang@intel.com>
Signed-off-by: Hongyu Zhang <hongyu.zhang@intel.com>
Signed-off-by: Wang LiangX <liangx.wang@intel.com>