Clarify which timeout was reached
Clarify which timeout was reached

When looking at varnishlog it looks like it is send_timeout that was reached,
but in fact it is idle_send_timeout. Clarify the language so the user
understands which parameter to adjust.

ssm/pkg-varnish,ssm/pkg-varnish,ssm/pkg-varnish,ssm/pkg-varnish,ssm/pkg-varnish