Missing lib for bazel built drake_visualizer.

[brandon-northcutt]

In testing the bazel built drake_visualizer

bazel build //tools:drake_visualizer && ./bazel-bin/tools/drake_visualizer

I received the error:

INFO: Running command line: bazel-bin/tools/drake_visualizer
external/director/bin/drake-visualizer: error while loading shared libraries: libQt5Multimedia.so.5: cannot open shared object file: No such file or directory
ERROR: Non-zero return code '127' from command: Process exited with status 127.

This was alleviated by adding libqt5multimedia5 to the package list in setup/ubuntu/16.04/install_prereqs.sh. This is following on from #6259 #6319 and should be blocking for my pending docker PR #6196 so that pretty visualizations are possible.

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[jwnimmer-tri]

Thanks!

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