Link custom apt sources to /etc/apt/sources.list.d/ directory
Link custom apt sources to /etc/apt/sources.list.d/ directory

Previously, we appended the contents of our apt-source-append.list to the /etc/apt/sources.list file, which caused problems on multiple `vagrant provision` commands unless we also took over the entire list by using our apt-source-default.list file.

Because multiple .list files can be specified in the /etc/apt/sources.list.d/ directory, this is a much better option for us.

rpkoller/VVV,erikjoling/VVV,Varying-Vagrant-Vagrants/VVV,morganestes/VVV,tu-software-studio/VVV,TobiasBg/Varying-Vagrant-Vagrants,jjogle/VVV,tim-steele/VVV,jjogle/VVV,salcode/VVV,thatmitchcanter/VVV-Lite,zaantar/vov,mattbanks/VVV,cristovaov/VVV,patrickheeney/VVV,miya0001/VVV,startsiden/lokalhero-wordpress-vagrant,erikjoling/VVV,lkwdwrd/varying-vagrant-vagrants,saucal/VVV,thatmitchcanter/VVV-Lite,jcgsville/iProcrastinated,startsiden/lokalhero-wordpress-vagrant,tomjn/varying-vagrant-vagrants,Haimanot1989/vvv-at-senitel,evelynriossf/VVV-MultiMachine,rogeruiz/VVV,grantnorwood/VVV,rpkoller/VVV,ezekg/theme-juice-vvv,lkwdwrd/varying-vagrant-vagrants,commana/moodle-vagrant,usminteractive/VVV,harvestweb/VVV,tpkemme/TVV,primozcankar/VVV,rooftopcms/VVV,ericandrewlewis/VVV,bitclaw/VVV,EHLOVader/VVV,tttanaka/VVV,namminammi/VVV,BlakeRxxk/VVV,saucal/VVV,tim-steele/VVV,mattbanks/VVV,namminammi/VVV,hellquist/vvv,AngeIII/VVV-Simplified,morganestes/VVV,evelynriossf/VVV-MultiMachine,taupecat/VVV,designreuse/VVV,saucal/VVV,Varying-Vagrant-Vagrants/VVV,Varying-Vagrant-Vagrants/VVV,tomjn/varying-vagrant-vagrants,iparr/VVV,thatmitchcanter/VVV-Lite,n2linux/VVV,DrewAPicture/varying-vagrant-vagrants,patrickheeney/VVV,commana/moodle-vagrant,speartail/VVV,AngeIII/VVV-Simplified,mikesprague/VVV,trepmal/varying-vagrant-vagrants,killa-kyle/vvv,n2linux/VVV,Haimanot1989/vvv-at-senitel,rooftopcms/VVV,ryandury/VVV,ericmann/VVV,ryandury/VVV,clreed87/VVV,morganestes/VVV,peterblazejewicz/vvv-custom,DrewAPicture/varying-vagrant-vagrants,AngeIII/VVV-Simplified,tpkemme/TVV,tpkemme/TVV,ericmann/VVV,BlakeRxxk/VVV,digitalmediaproduction/JAMAVagrant,rogeruiz/VVV,miya0001/VVV,trepmal/varying-vagrant-vagrants,AngeIII/VVV-Simplified,harvestweb/VVV,nexusthemes/VVV,taupecat/VVV,jjeaton/VVV,tu-software-studio/VVV,EHLOVader/VVV,enriquezm/VVV,cfoellmann/VVV,ezekg/VVV,taupecat/VVV,killa-kyle/vvv,writecodedrinkcoffee/VVV,mattbanks/VVV,grantnorwood/VVV,jjeaton/VVV,clreed87/VVV,peterblazejewicz/vvv-custom,zaantar/vov,primozcankar/VVV,writecodedrinkcoffee/VVV,tttanaka/VVV,designreuse/VVV,WybrenKoelmans/VVV,ezekg/theme-juice-vvv,hellquist/vvv,speartail/VVV,nexusthemes/VVV,bitclaw/VVV,usminteractive/VVV,salcode/VVV,startsiden/lokalhero-wordpress-vagrant,TobiasBg/Varying-Vagrant-Vagrants,tu-software-studio/VVV,ezekg/VVV,jcgsville/iProcrastinated,digitalmediaproduction/JAMAVagrant,iparr/VVV,tpkemme/TVV,cristovaov/VVV,WybrenKoelmans/VVV,AngeIII/VVV-Simplified,mikesprague/VVV,startsiden/lokalhero-wordpress-vagrant,westi/varying-vagrant-vagrants,enriquezm/VVV,taupecat/VVV,westi/varying-vagrant-vagrants,cfoellmann/VVV,tu-software-studio/VVV,ericandrewlewis/VVV