This reverts commit b8a0ea97.

I'm not convinced that we want to prevent reloaded VCLs to cool down
after subsequent reloads.

Otherwise the warmup delay might be ineffective.

Introduce a -h option for a usage more discoverable.

After feedback from @ssm.

The output of vcl.discard is ignored because it's a blank line, so
instead the script forges a message. In case of failure, the error
message is still displayed.

Confirmed by testing the behavior of various varnish versions.

If a VCL was reloaded at the date of this commit, it would change from:

    reload_20170321T174643

to

    reload_20170321_174643

This gives second resolution to the reload's name but keeps the name
compact, parseable, and naturally sorted. An example is displayed with
the usage error message.

It was there to test a failure...