fixing create_image

create_image was consistently returning errors even when the image creation was successful. this was because the docker daemon (docker version 20.10.14) adds line returns and carriage returns between each section. This made replacing "}{" with "},{" fail, since now we have "}\r\n{" instead. So I simply removed all the "\r" and "\n" before the previous fix.

Also replaced the String arguments with &str. Functionally similar but better rust practice IMO.