make --retry option identical the one in curl

[fabricereix]

Currently, --retry option in Hurl does not exactly have the same semantic than the --retry option in curl.
In curl, it specify the number of retries (0 by default = no retry)
while in Hurl, it just means "keep retrying" and the number of retries is given by the option --retry-max-count.

We are going to align Hurl behavior to curl.
It is still interesting to have the possibility to retry indefinitely.
Maybe by passing the value -1.
This is consistent with --max-redirs (Set this option to -1 to make it unlimited)