Unclear error message when user creates image with incorrect location url

[Timur Nurlygayanov]

Steps To Reproduce:
1. Login to Horizon dashboard
2. Navigate to Project > Compute > Images
3. Click on "Create Image" button
4. Set name for this image = "test", Image Source = "Image Location", Image Location = "http://test2.com/this-image-doesn't-exists.qcow2", Format = "QCOW2"
5. Click on "Create Image"

Expected Result:
Horizon should validate the url and provide warning message about the incorrect url or at least show error message after "create image" dialog will be closed.

Observed Result:
The dialog window is active and we can see the following error on the background (and it is not clear why we can't create the image):
Error: Unable To Create New Image

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/319839

[OpenStack Infra (hudson-openstack)]

Change abandoned by Rob Cresswell (<email address hidden>) on branch: master
Review: https://review.openstack.org/319839
Reason: Abandoned due to inactivity

[Gary W. Smith (gary-w-smith)]

It is possible that the network configuration would permit glance to access the URL but not horizon. If such a check is added to horizon, then it should be a warning rather than a hard error.

[Vishal Manchanda (vishalmanchanda)]

as no one was active on this bug, so assigned it to myself.

[Vishal Manchanda (vishalmanchanda)]

will cover this bug in the refactor-error-message blueprint(https://blueprints.launchpad.net/horizon/+spec/refactor-error-messages)