MINOR: cfgparse: always alloc idle conns task

MINOR: cfgparse: always alloc idle conns task

The idle conn task is is a global task used to cleanup backend
connections marked for deletion. Previously, it was only only allocated
if at least one server in the configuration has idle connections.

This assumption won't be valid anymore when new servers can be created
at runtime with idle connections. Always allocate the global idle conn
task.