[YouTube] Honor --include-ads (was: --include-ads should work with -g)

[ghost]

• [x ] I've verified and I assure that I'm running youtube-dl 2016.09.15
• [x ] At least skimmed through README and most notably FAQ and BUGS sections
• [ x] Searched the bugtracker for similar issues including closed ones

What is the purpose of your issue?

• [ x] Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
• [x ] Feature request (request for a new functionality)
• Question
• Other

If the purpose of this issue is a bug report, site support request or you are not completely sure provide the full verbose output as follows:

$ youtube-dl -v --include-ads -g https://www.youtube.com/watch?v=by1RRP9wa_Y
[debug] System config: []
[debug] User config: []
[debug] Command-line args: ['--prefer-free-formats', '-v', '--include-ads', '-g', 'https://www.youtube.com/watch?v=by1RRP9wa_Y']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2016.09.15
[debug] Python version 3.5.2 - Linux-4.4.20-1-lts-x86_64-with-arch
[debug] exe versions: ffmpeg 3.1.3, ffprobe 3.1.3, rtmpdump 2.4
https://r6---sn-n4g-jqb6.googlevideo.com/videoplayback?sparams=clen%2Cdur%2Cei%2Cgcr%2Cgir%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Ckeepalive%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cpcm2cms%2Cpl%2Crequiressl%2Csource%2Cupn%2Cexpire&ei=XuvbV4LlHam9iQbl9pyYCg&ip=77.158.88.42&clen=26041709&id=o-AKiNrGp651rPkcaCPGxWujOUygseRQXH2xoIUTBSuRPy&keepalive=yes&upn=QmaIi7k2-PE&mm=31&mn=sn-n4g-jqb6&mt=1474029834&mv=m&ms=au&itag=135&ipbits=0&lmt=1469864873129722&expire=1474052030&mime=video%2Fmp4&key=yt6&gir=yes&requiressl=yes&source=youtube&gcr=fr&pcm2cms=yes&dur=253.240&initcwndbps=1521250&pl=21&signature=C914E7A617EB00B7135B91A92C02E636AA7D3523.8C8172EB1A25A5B4B245B73FFAC5C391F76622E3&ratebypass=yes
https://r6---sn-n4g-jqb6.googlevideo.com/videoplayback?sparams=clen%2Cdur%2Cei%2Cgcr%2Cgir%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Ckeepalive%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cpcm2cms%2Cpl%2Crequiressl%2Csource%2Cupn%2Cexpire&ei=XuvbV4LlHam9iQbl9pyYCg&ip=77.158.88.42&clen=4015657&id=o-AKiNrGp651rPkcaCPGxWujOUygseRQXH2xoIUTBSuRPy&keepalive=yes&upn=QmaIi7k2-PE&mm=31&mn=sn-n4g-jqb6&mt=1474029834&mv=m&ms=au&itag=251&ipbits=0&lmt=1469722106914133&expire=1474052030&mime=audio%2Fwebm&key=yt6&gir=yes&requiressl=yes&source=youtube&gcr=fr&pcm2cms=yes&dur=253.261&initcwndbps=1521250&pl=21&signature=BE56DEA07BCF75742743076F0B86570EFE4D9ED6.3C87F915F1312A22E5C500EA98DB9B4222AE9AE0&ratebypass=yes
...
<end of log>

Description of your issue, suggested solution and other information

When using -g option to get video url and --include-ads option, youtube-dl should include ads url too.

I'm using youtube-dl in lollypop to allow users playing music from youtube but I will prefer to add a "fair use" by default (playing ads) with an hidden option to disable ads.

[yan12125]

Currently --include-ads works with Brightcove only. YouTube support is not implemented yet.