repo: Handle parent repos with different remote configuration

repo: Handle parent repos with different remote configuration

In the case we have a repo with a parent, and the child repo has a
remote called "foo", but some option is unset. Then when we look up
the parent repo for a value before using the default we will fail due
to the parent not having the "foo" remote. As soon as we find the
requested remote at some point in the hierarchy we need to ignore further
errors and use the default value.

Closes: #274
Approved by: giuseppe