This allows overriding the name used of the file in google storage,
image name or instance name. This will vary depending on how much `moby
run` is doing which is goverened by whether the positional argument
contains an `.img.tar.gz` or not.
For example:
`moby run gcp -img-name test-ea34d1 test` creates an instance called
`test-ea34d1` from the image `test`
`moby run gcp -img-name test-ea34d1` test.img.tar.gz` will upload the
file as `test-ea34d1.tar.gz`, create image `test-ea34d1` and create an
instance called `test-ea34d1`.
The use case for this is for CI to be able to spawn many concurrent test
machines and provide it's own name for them.
Signed-off-by: Dave Tucker <dt@docker.com>