build: Correct erroneous test for squashfs-tools
build: Correct erroneous test for squashfs-tools

The `scripts/vagrant/install-rkt.sh` script erroneously tests for the
existence of a `unsquash` command. It should be `unsquashfs` instead.

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