functional tests: add GC-after-unmount test
functional tests: add GC-after-unmount test

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