If the storage service url has trailing slash the fetch command will fail

[peterVG]

If the url for a configured storage service contains a trailing / character, then when we come to append the api command here, we'll get a double // which causes the command to fail.

[ross-spencer]

Related #7 the ticket says it all, so as we fix this up and bring in AMClient we might find working with paths like this a lot easier.

[peterVG]

I can fix this with a simple form validation for now. Refactoring to use AMClient is a good suggestion but not trivial at this stage.

[ross-spencer]

Tiny fix for this and tests here c1eb647 there might be a better long-term solution. This is useful to fix now as it helps with copy and paste.

[ross-spencer]

Continuing that fix here, it needed a little more effort: 852e3d2