Polling for download containers resolves when still in downloading status

[jonasvekeman]

When an GCL downloads several containers the status goes from downloading to installed, the javascript library should wait for using that container until the download has finished.
Current issue is that the javascript library uses the container when it is still downloading, resulting in an error.
This can be reproduced by uninstalling the GCL and going to RMC and installing while on the application and being on a slow network(this will slow down the downloading process).

[jonasvekeman]

Duplicate of #51