tests: add rkt_fetch_test.go
tests: add rkt_fetch_test.go

This will test that 'rkt fetch' will bypass the on-disk store,
and 'rkt run/prepare' will bypass the on-disk store if tag is 'latest'
or scheme is 'file'.

Also increase the test timeout.

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