provision/docker: valid image names return empty if no img is available
provision/docker: valid image names return empty if no img is available

gciotta/tsuru,guilhermebr/tsuru,ArxdSilva/tsuru,jblancett/tsuru,guilhermebr/tsuru,jblancett/tsuru,cezarsa/tsuru,RichardKnop/tsuru,mderaldo/tsuru,hcxiong/tsuru,gciotta/tsuru,cgvarela/tsuru,4eek/tsuru,firebitsbr/tsuru,cgvarela/tsuru,kgrvamsi/tsuru,jblancett/tsuru,gwmoura/tsuru,Endika/tsuru,mderaldo/tsuru,Endika/tsuru,tuxmonteiro/tsuru,hcxiong/tsuru,hcxiong/tsuru,RichardKnop/tsuru,ArxdSilva/tsuru,tuxmonteiro/tsuru,ArxdSilva/tsuru,firebitsbr/tsuru,cezarsa/tsuru,tsuru/tsuru,tsuru/tsuru,firebitsbr/tsuru,kgrvamsi/tsuru,ggarnier/tsuru,Endika/tsuru,4eek/tsuru,tsuru/tsuru,ggarnier/tsuru,tsuru/tsuru,guilhermebr/tsuru,cezarsa/tsuru,cezarsa/tsuru,ArxdSilva/tsuru,guilhermebr/tsuru,4eek/tsuru,gwmoura/tsuru,hugoantunes/tsuru,cgvarela/tsuru,tuxmonteiro/tsuru,gwmoura/tsuru,ggarnier/tsuru,gciotta/tsuru,mderaldo/tsuru,kgrvamsi/tsuru,ggarnier/tsuru,hugoantunes/tsuru,RichardKnop/tsuru