Merge branch 'dl/credential-cache-socket-in-xdg-cache' into maint

Merge branch 'dl/credential-cache-socket-in-xdg-cache' into maint

A recently added test for the "credential-cache" helper revealed
that EOF detection done around the time the connection to the cache
daemon is torn down were flaky.  This was fixed by reacting to
ECONNRESET and behaving as if we got an EOF.

* dl/credential-cache-socket-in-xdg-cache:
  credential-cache: interpret an ECONNRESET as an EOF