Add a retry if "METAMON" met with 500 error

[Ixve]

If metamon gets an error 500 while creating a repository - it should automatically retry after ~5s.

If persistently met with this error - it shouldn't print out the HTML response text like it does and instead should shorten it down to a simple explanation text.

While this error is quite rare - it would still be a nice enhancement to the project.