Mount will time out for large archives when the index is not yet built

[azehe]

At first mount, ratarmount builds an index from the archive.
This takes a long time for large archives and will lead to a mount timeout in kubernetes. We need to find a way to work around that, optimally with a progress report in the Pod description.

Quickfix: Mount the archive once on a host directly, which builds the index. This can only be done by an admin.

[dr-ankr]

Update to the quickfix: users can mount tars themselves on vingilot after installing ratarmount with pip.