provision/docker: better error message when trying to push image
provision/docker: better error message when trying to push image

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