Fix getImagesJSON output for api less than 1.7

Tag can be a number, like centos:6.4, and so must be handled like a
string otherwise will lose quotation marks when converting to json
and the client (API < 1.7) will try to convert to int, failing
because the type is string. Additionally using ParseRepositoryTag to
parse repository names to split the tag because an URL can have : and
so more than one occurrence of : can be found on repository names.

Docker-DCO-1.1-Signed-off-by: Fabio Falci <fabiofalci@gmail.com> (github: fabiofalci)
Update package for repo and tag parser
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Merge pull request #7362 from crosbymichael/fix-get-image-json

Fix get image json