test possible audio input to write_videofile

[thenewguy]

Provides tests for #876 and #1032

Intends to supersede #919 and #968

[coveralls]

Coverage decreased (-0.2%) to 64.69% when pulling 0d9fb0b on thenewguy:apply-audio-removal-to-ffmpeg-input into c962808 on Zulko:master.

[coveralls]

Coverage remained the same at 64.842% when pulling 1bbcd89 on thenewguy:apply-audio-removal-to-ffmpeg-input into c962808 on Zulko:master.

[thenewguy]

These tests are passing - perhaps those issues are really about manually adding audio with extra ffmpeg parameters? Or maybe it is something to do with ffmpeg versions.

Anyways, I could not find write_videofile() audio options included anywhere in the tests so these should be merged.

[thenewguy]

Closing in favor of #1039