splits FFMPEG::Transcoder#run method into #transcode_movie and #validate_output_file

it enables to option to run the transcoding without validating if single output file is created, which is required for 'HLS segmentation'
HLS segmentation will create multiple output files, so validation for 1 specific file isn't required.
adds spec for audio only transcoding with ffmpeg 1.0.1
fixes ffmpeg 1.0.1 audio only transcoding
Merge branch 'add_conditional_error_check' into develop
Merge branch 'audio_only_stranscoding_bug' into develop