rkt: add appc spec version information
rkt: add appc spec version information

`rkt version` should print not only its own version, but version
information for the spec against which it is built.

squaremo/rkt,liubq919/rkt,tv42/rkt,jakon89/rkt,joshix/rkt,michelangelo13/rkt,xnox/rkt,dalanlan/rkt,rkt/rkt,bsmr-go/rkt,sinfomicien/rkt,matthaias/rkt,krnowak/rkt,MabinGo/rkt,robszumski/rocket,mjg59/rkt,tv42/rkt,wparad/rkt,akshaykarle/rkt,ChengTiesheng/rkt,eyakubovich/rkt,squeed/rkt,rhvgoyal/rkt,jonboulle/rkt,yifan-gu/rkt,lucasallan/rkt,cab105/rkt,fdserr/rkt,MattDees/rkt,Wilybald/rkt,MabinGo/rkt,dgonyeo/rkt,lucasallan/rkt,mjg59/rkt,tmrts/rkt,chrisseto/rkt,Yhgenomics/rkt,adfernandes/rkt,rot26/rkt,ramitsurana05/rkt,matthaias/rkt,intfrr/rkt,iankronquist/rkt,mattthias/pkg-rkt,bsmr-go/rkt,Shashwatsh/rkt,coreos/rkt,ybubnov/rkt,yifan-gu/rkt,robszumski/rocket,smarvin/rkt,MabinGo/rkt,intelsdi-x/rkt,squaremo/rkt,dgonyeo/rkt,achanda/rkt,kinvolk/rkt,jjlakis/rkt,MattDees/rkt,rhvgoyal/rkt,Wilybald/rkt,blixtra/rkt,adfernandes/rkt,joshix/rkt,dalanlan/rkt,Shashwatsh/rkt,clearlinux/rkt,joshix/rkt,coreos/rkt,monstermunchkin/rkt,liugenping/rkt,akshaykarle/rkt,ChengTiesheng/rkt,lee212/rkt,achanda/rkt,rkt/rkt,lee212/rkt,jasonchaffee/rkt,intelsdi-x/rkt,Shashwatsh/rkt,squaremo/rkt,s-urbaniak/rkt,jakon89/rkt,crawford/rkt,alban/rkt,achanda/rkt,yifan-gu/rocket,lsm5/rkt,blixtra/rkt,markllama/rkt,jonboulle/rkt,alban/rkt,rkt/rkt,lucasallan/rkt,mattthias/pkg-rkt,sstabellini/rkt,jzelinskie/rkt,jjlakis/rkt,jasonchaffee/rkt,alban/rkt,marineam/rkt,coreos/rkt,bsmr-go/rkt,joshix/rkt,markllama/rkt,luebken/rkt,shobhit85/rkt,tixxdz/rkt,fdserr/rkt,mike1729/rkt,dgonyeo/rkt,liubq919/rkt,klizhentas/rkt,sinfomicien/rkt,markllama/rkt,mike1729/rkt,klizhentas/rkt,Yhgenomics/rkt,monstermunchkin/rkt,robszumski/rocket,Wilybald/rkt,smarvin/rkt,iaguis/rkt,kinvolk/rkt,rhvgoyal/rkt,kinvolk/rkt,nhlfr/rkt,dalanlan/rkt,s-urbaniak/rkt,endocode/rkt,eyakubovich/rkt,blixtra/rkt,jzelinskie/rkt,tixxdz/rkt,shtouff/rkt,intelsdi-x/rkt,liubq919/rkt,kbrwn/rkt,krnowak/rkt,shtouff/rkt,nhlfr/rkt,michelangelo13/rkt,krnowak/rkt,s-urbaniak/rkt,luebken/rkt,il9ue/rkt,ybubnov/rkt,lsm5/rkt,mjg59/rkt,sgotti/rkt,sstabellini/rkt,yifan-gu/rkt,alexhersh/rkt,crawford/rkt,iaguis/rkt,jjlakis/rkt,euank/rkt,ChengTiesheng/rkt,rot26/rkt,yifan-gu/rocket,fdserr/rkt,MattDees/rkt,wparad/rkt,alexhersh/rkt,marineam/rkt,matthaias/rkt,lsm5/rkt,ramitsurana/rkt,tv42/rkt,clearlinux/rkt,xnox/rkt,jasonchaffee/rkt,nhlfr/rkt,shobhit85/rkt,klizhentas/rkt,ramitsurana05/rkt,mike1729/rkt,ramitsurana/rkt,ramitsurana/rkt,Yhgenomics/rkt,Wilybald/rkt,cab105/rkt,mattthias/pkg-rkt,squeed/rkt,shobhit85/rkt,jzelinskie/rkt,il9ue/rkt,intfrr/rkt,squeed/rkt,luebken/rkt,sinfomicien/rkt,chrisseto/rkt,liugenping/rkt,tmrts/rkt,kbrwn/rkt,kbrwn/rkt,adfernandes/rkt,michelangelo13/rkt,sgotti/rkt,il9ue/rkt,shtouff/rkt,lee212/rkt,kinvolk/rkt,crawford/rkt,alexhersh/rkt,smarvin/rkt,lucasallan/rkt,wparad/rkt,marineam/rkt,linki/rkt,endocode/rkt,jakon89/rkt,akshaykarle/rkt,rot26/rkt,maquanyi/rkt,jonboulle/rkt,iaguis/rkt,endocode/rkt,cab105/rkt,tixxdz/rkt,maquanyi/rkt,clearlinux/rkt,eyakubovich/rkt,chrisseto/rkt,sstabellini/rkt,euank/rkt,linki/rkt,linki/rkt,ramitsurana05/rkt,sgotti/rkt,yifan-gu/rocket,euank/rkt,xnox/rkt,maquanyi/rkt,ybubnov/rkt,liugenping/rkt,iankronquist/rkt,iankronquist/rkt,tmrts/rkt,rkt/rkt,monstermunchkin/rkt,intfrr/rkt