Previously only files specified in the ConfigMap were checked for
changed modification times. If only generated VCL sources were
changed, usually due to Endpoint changes, and the VCL load failed
for any reason, tehn afterward no changed VCL sources or changes
in the ConfigMap were detected. This could lead to VCL never being
updated after a change only in the generated VCLs, although the
config does not correspond to the desired state of the cluster.

Now we keep a record of the latest mtime of all VCL sources,
including generated sources, and reload VCL if any of them are
currently newer.