collector: improve code
collector: improve code

running separate goroutine for each collector (one for ec2 and other for
juju). No synchronization needed :)

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