This commit improves the fallback behaviour when resolving and
fetching images with multiple hosts. If an error is encountered
when resolving and fetching images, and more than one host is being
used, we will try the same operation on the next host. The error
from the first host is preserved so that if all hosts fail, we can
display the error from the first host.
fixes#3850
Signed-off-by: Alex Price <aprice@atlassian.com>