Use variable to choose between vp8 and vp9 in ab_compare_libvpx.sh.
Use variable to choose between vp8 and vp9 in ab_compare_libvpx.sh.

nvoron23/daala,HeadhunterXamd/daala,kodabb/daala,ycho/daala,vr000m/daala,kustom666/daala,jmvalin/daala,mbebenita/daala,ascent12/daala,ascent12/daala,ascent12/daala,ascent12/daala,vr000m/daala,mbebenita/daala,ycho/daala,xiph/daala,jmvalin/daala,xiphmont/daala,kodabb/daala,kodabb/daala,mbebenita/daala,kodabb/daala,luctrudeau/daala,iankronquist/daala,xiph/daala,KyleSiefring/daala,iankronquist/daala,ycho/daala,xiphmont/daala,kustom666/daala,felipebetancur/daala,jmvalin/daala,luctrudeau/daala,nvoron23/daala,iankronquist/daala,luctrudeau/daala,vr000m/daala,HeadhunterXamd/daala,nvoron23/daala,felipebetancur/daala,iankronquist/daala,mbebenita/daala,KyleSiefring/daala,felipebetancur/daala,vr000m/daala,mbebenita/daala,luctrudeau/daala,vr000m/daala,felipebetancur/daala,xiphmont/daala,kustom666/daala,tribouille/daala,xiphmont/daala,felipebetancur/daala,xiph/daala,luctrudeau/daala,tribouille/daala,KyleSiefring/daala,xiph/daala,kodabb/daala,tribouille/daala,kustom666/daala,tribouille/daala,kustom666/daala,KyleSiefring/daala,HeadhunterXamd/daala,jmvalin/daala,HeadhunterXamd/daala,iankronquist/daala,xiphmont/daala,ycho/daala,KyleSiefring/daala,nvoron23/daala,ycho/daala,ascent12/daala,nvoron23/daala,tribouille/daala,HeadhunterXamd/daala,jmvalin/daala,xiph/daala