ostree/pull: Add network-retries command line option

This exposes a way to specify from the command line the number
of times to retry each download after a network error. If a negative
value is given, then the default number of retries (5) is used. If 0
is given, then errors are returned without retrying.

closes #1659

Closes: #1669
Approved by: jlebon

bash/ostree

@@ -908,6 +908,7 @@ _ostree_pull() {
         --depth
         --http-header
         --localcache-repo -L
+        --network-retries
         --repo
         --subpath
         --update-frequency