If plugins are disabled, report them as not available.
If plugins are disabled, report them as not available.

Allows usage of VAGRANT_NO_PLUGINS env var to disable plugins.

Fixes #5430.

mwrock/vagrant,krig/vagrant,benh57/vagrant,jean/vagrant,crashlytics/vagrant,gbarberi/vagrant,wangfakang/vagrant,sni/vagrant,kamigerami/vagrant,Chhed13/vagrant,muhanadra/vagrant,gitebra/vagrant,mkuzmin/vagrant,mkuzmin/vagrant,gpkfr/vagrant,crashlytics/vagrant,johntron/vagrant,dhoer/vagrant,nickryand/vagrant,jhoblitt/vagrant,bdwyertech/vagrant,aneeshusa/vagrant,h4ck3rm1k3/vagrant,Sgoettschkes/vagrant,janek-warchol/vagrant,johntron/vagrant,myrjola/vagrant,nickryand/vagrant,genome21/vagrant,denisbr/vagrant,krig/vagrant,mitchellh/vagrant,lukebakken/vagrant,shtouff/vagrant,darkn3rd/vagrant,philoserf/vagrant,doy/vagrant,jtopper/vagrant,mitchellh/vagrant,dustymabe/vagrant,blueyed/vagrant,bheuvel/vagrant,vamegh/vagrant,signed8bit/vagrant,tschortsch/vagrant,denisbr/vagrant,carlosefr/vagrant,jberends/vagrant,jmanero/vagrant,dhoer/vagrant,aaam/vagrant,marxarelli/vagrant,jberends/vagrant,PatOShea/vagrant,jhoblitt/vagrant,bryson/vagrant,pwnall/vagrant,Chhunlong/vagrant,modulexcite/vagrant,pwnall/vagrant,nickryand/vagrant,Sgoettschkes/vagrant,apertoso/vagrant,philwrenn/vagrant,modulexcite/vagrant,mwarren/vagrant,jean/vagrant,ferventcoder/vagrant,dustymabe/vagrant,mwrock/vagrant,gitebra/vagrant,ArloL/vagrant,bryson/vagrant,mwarren/vagrant,Endika/vagrant,jberends/vagrant,Chhunlong/vagrant,modulexcite/vagrant,blueyed/vagrant,jberends/vagrant,sax/vagrant,PatOShea/vagrant,mpoeter/vagrant,pwnall/vagrant,mpoeter/vagrant,carlosefr/vagrant,chrisvire/vagrant,lonniev/vagrant,ArloL/vagrant,benh57/vagrant,genome21/vagrant,gbarberi/vagrant,kamigerami/vagrant,gbarberi/vagrant,jtopper/vagrant,myrjola/vagrant,benh57/vagrant,blueyed/vagrant,justincampbell/vagrant,loren-osborn/vagrant,signed8bit/vagrant,invernizzi-at-google/vagrant,Avira/vagrant,gpkfr/vagrant,jfchevrette/vagrant,signed8bit/vagrant,pwnall/vagrant,johntron/vagrant,aneeshusa/vagrant,gpkfr/vagrant,lonniev/vagrant,jmanero/vagrant,justincampbell/vagrant,bdwyertech/vagrant,jean/vagrant,gpkfr/vagrant,gbarberi/vagrant,tbriggs-curse/vagrant,bdwyertech/vagrant,ferventcoder/vagrant,Avira/vagrant,stephancom/vagrant,petems/vagrant,aneeshusa/vagrant,TheBigBear/vagrant,sni/vagrant,benizi/vagrant,chrisvire/vagrant,jean/vagrant,Endika/vagrant,Sgoettschkes/vagrant,tschortsch/vagrant,senglin/vagrant,jmanero/vagrant,ferventcoder/vagrant,justincampbell/vagrant,PatrickLang/vagrant,dharmab/vagrant,kamazee/vagrant,ferventcoder/vagrant,taliesins/vagrant,cgvarela/vagrant,TheBigBear/vagrant,Endika/vagrant,ianmiell/vagrant,wangfakang/vagrant,chrisvire/vagrant,krig/vagrant,justincampbell/vagrant,tbarrongh/vagrant,jfchevrette/vagrant,wkolean/vagrant,kalabiyau/vagrant,PatOShea/vagrant,invernizzi-at-google/vagrant,kamazee/vagrant,sax/vagrant,benizi/vagrant,tomfanning/vagrant,chrisvire/vagrant,fnewberg/vagrant,fnewberg/vagrant,stephancom/vagrant,jhoblitt/vagrant,lukebakken/vagrant,johntron/vagrant,nickryand/vagrant,wkolean/vagrant,bshurts/vagrant,wangfakang/vagrant,fnewberg/vagrant,taliesins/vagrant,mkuzmin/vagrant,PatrickLang/vagrant,sni/vagrant,ianmiell/vagrant,lukebakken/vagrant,jkburges/vagrant,mitchellh/vagrant,h4ck3rm1k3/vagrant,jtopper/vagrant,mitchellh/vagrant,kamigerami/vagrant,Chhunlong/vagrant,wkolean/vagrant,bheuvel/vagrant,tjanez/vagrant,invernizzi-at-google/vagrant,apertoso/vagrant,benh57/vagrant,sax/vagrant,zsjohny/vagrant,bshurts/vagrant,gitebra/vagrant,tbriggs-curse/vagrant,ianmiell/vagrant,mwarren/vagrant,tomfanning/vagrant,zsjohny/vagrant,myrjola/vagrant,dustymabe/vagrant,kamazee/vagrant,h4ck3rm1k3/vagrant,TheBigBear/vagrant,tomfanning/vagrant,senglin/vagrant,Sgoettschkes/vagrant,zsjohny/vagrant,senglin/vagrant,teotihuacanada/vagrant,tschortsch/vagrant,doy/vagrant,bshurts/vagrant,chrisroberts/vagrant,invernizzi-at-google/vagrant,doy/vagrant,doy/vagrant,vamegh/vagrant,darkn3rd/vagrant,dharmab/vagrant,dustymabe/vagrant,philwrenn/vagrant,Chhunlong/vagrant,jtopper/vagrant,tjanez/vagrant,cgvarela/vagrant,PatOShea/vagrant,bheuvel/vagrant,dharmab/vagrant,marxarelli/vagrant,lonniev/vagrant,ArloL/vagrant,tbriggs-curse/vagrant,bheuvel/vagrant,sax/vagrant,jfchevrette/vagrant,jkburges/vagrant,ArloL/vagrant,myrjola/vagrant,wangfakang/vagrant,Avira/vagrant,janek-warchol/vagrant,dhoer/vagrant,teotihuacanada/vagrant,patrys/vagrant,Avira/vagrant,philoserf/vagrant,kalabiyau/vagrant,teotihuacanada/vagrant,mkuzmin/vagrant,modulexcite/vagrant,stephancom/vagrant,blueyed/vagrant,vamegh/vagrant,wkolean/vagrant,petems/vagrant,tomfanning/vagrant,shtouff/vagrant,tjanez/vagrant,carlosefr/vagrant,chrisroberts/vagrant,PatrickLang/vagrant,mwrock/vagrant,philwrenn/vagrant,lukebakken/vagrant,patrys/vagrant,teotihuacanada/vagrant,Chhed13/vagrant,muhanadra/vagrant,kamigerami/vagrant,bdwyertech/vagrant,philwrenn/vagrant,loren-osborn/vagrant,petems/vagrant,aaam/vagrant,benizi/vagrant,dharmab/vagrant,cgvarela/vagrant,tschortsch/vagrant,h4ck3rm1k3/vagrant,genome21/vagrant,lonniev/vagrant,mwrock/vagrant,gitebra/vagrant,shtouff/vagrant,crashlytics/vagrant,dhoer/vagrant,stephancom/vagrant,loren-osborn/vagrant,janek-warchol/vagrant,aaam/vagrant,patrys/vagrant,marxarelli/vagrant,tjanez/vagrant,taliesins/vagrant,apertoso/vagrant,Chhed13/vagrant,aaam/vagrant,kalabiyau/vagrant,mpoeter/vagrant,tbarrongh/vagrant,benizi/vagrant,fnewberg/vagrant,ianmiell/vagrant,muhanadra/vagrant,philoserf/vagrant,Chhed13/vagrant,jkburges/vagrant,jfchevrette/vagrant,petems/vagrant,PatrickLang/vagrant,bryson/vagrant,mwarren/vagrant,Endika/vagrant,marxarelli/vagrant,cgvarela/vagrant,muhanadra/vagrant,janek-warchol/vagrant,bryson/vagrant,kamazee/vagrant,carlosefr/vagrant,crashlytics/vagrant,mpoeter/vagrant,genome21/vagrant,kalabiyau/vagrant,aneeshusa/vagrant,denisbr/vagrant,zsjohny/vagrant,loren-osborn/vagrant,tbarrongh/vagrant,TheBigBear/vagrant,philoserf/vagrant,taliesins/vagrant,jkburges/vagrant,jhoblitt/vagrant,chrisroberts/vagrant,sni/vagrant,senglin/vagrant,jmanero/vagrant,krig/vagrant,chrisroberts/vagrant,bshurts/vagrant,shtouff/vagrant,tbriggs-curse/vagrant,signed8bit/vagrant,darkn3rd/vagrant,tbarrongh/vagrant,apertoso/vagrant,denisbr/vagrant,darkn3rd/vagrant,vamegh/vagrant,patrys/vagrant