rkt: always use https:// when fetching docker images
rkt: always use https:// when fetching docker images

The insecure parameter forces docker2aci to connect to the registry
using `http://`.

Make it false while docker2aci doesn't have logic to try `https://` and
fall back to `http://` if that didn't work.

il9ue/rkt,linki/rkt,sinfomicien/rkt,joshix/rkt,markllama/rkt,matthaias/rkt,squeed/rkt,yifan-gu/rkt,coreos/rkt,jasonchaffee/rkt,squeed/rkt,jjlakis/rkt,matthaias/rkt,Wilybald/rkt,sgotti/rkt,krnowak/rkt,cab105/rkt,sinfomicien/rkt,jjlakis/rkt,euank/rkt,s-urbaniak/rkt,jakon89/rkt,Wilybald/rkt,jakon89/rkt,dgonyeo/rkt,sgotti/rkt,il9ue/rkt,kinvolk/rkt,akshaykarle/rkt,euank/rkt,rkt/rkt,achanda/rkt,alban/rkt,shobhit85/rkt,lucasallan/rkt,endocode/rkt,kbrwn/rkt,sstabellini/rkt,coreos/rkt,kbrwn/rkt,yifan-gu/rkt,yifan-gu/rkt,linki/rkt,Shashwatsh/rkt,Shashwatsh/rkt,nhlfr/rkt,matthaias/rkt,rkt/rkt,sstabellini/rkt,blixtra/rkt,alban/rkt,Wilybald/rkt,yifan-gu/rocket,jasonchaffee/rkt,Wilybald/rkt,ybubnov/rkt,rkt/rkt,intelsdi-x/rkt,jonboulle/rkt,joshix/rkt,jasonchaffee/rkt,shobhit85/rkt,jonboulle/rkt,monstermunchkin/rkt,yifan-gu/rocket,kinvolk/rkt,endocode/rkt,Shashwatsh/rkt,lucasallan/rkt,krnowak/rkt,kinvolk/rkt,rkt/rkt,mike1729/rkt,alban/rkt,akshaykarle/rkt,coreos/rkt,linki/rkt,il9ue/rkt,joshix/rkt,sinfomicien/rkt,endocode/rkt,dgonyeo/rkt,ybubnov/rkt,joshix/rkt,intelsdi-x/rkt,markllama/rkt,ybubnov/rkt,squeed/rkt,yifan-gu/rocket,kbrwn/rkt,tmrts/rkt,mike1729/rkt,blixtra/rkt,intelsdi-x/rkt,blixtra/rkt,dgonyeo/rkt,jakon89/rkt,euank/rkt,kinvolk/rkt,jjlakis/rkt,sgotti/rkt,jonboulle/rkt,mike1729/rkt,tmrts/rkt,lucasallan/rkt,achanda/rkt,cab105/rkt,sstabellini/rkt,monstermunchkin/rkt,nhlfr/rkt,tmrts/rkt,akshaykarle/rkt,s-urbaniak/rkt,monstermunchkin/rkt,shobhit85/rkt,lucasallan/rkt,nhlfr/rkt,achanda/rkt,cab105/rkt,krnowak/rkt,markllama/rkt,s-urbaniak/rkt