issue #301: Only list remote ISOs with valid URL

The remote ISO path may become invalid after some time and it prevents
user to create a template from it.
To avoid those kind of errors, only list the distros with valid URL.

Signed-off-by: Aline Manera <alinefm@br.ibm.com>
issue #301: Add a loading message while listing default remote ISOs

The remote ISO path may become invalid and we check it on backend to
only return valid data to UI.
But checking the remote ISO path for each distro can take some time so
UI needs to properly display it to user.
Do that by adding a loading message until get the backend response.

Also update the .po files as new messages were added.

Signed-off-by: Aline Manera <alinefm@br.ibm.com>
Update distros JSON files to always point to a valid URL

Although we only list the distros with a valid URL we need to make sure
to always package distros JSON files with a valid values.
So fix the URL's for Debian Wheezy and Gentoo

Signed-off-by: Aline Manera <alinefm@br.ibm.com>