Clarify gorouter job property max_idle_connections
Clarify gorouter job property max_idle_connections

The template for gorouter is as follows:

```
<% if p("router.max_idle_connections") && p("router.max_idle_connections") > 0 %>
disable_keep_alives: false
max_idle_conns: <%= p("router.max_idle_connections") %>
max_idle_conns_per_host: 100
endpoint_keep_alive_probe_interval: <%= p("router.keep_alive_probe_interval") %>
<% else %>
disable_keep_alives: true
<% end%>
```

i.e. when max_idle_connections is set and greater than zero then:

- we use that for the total number of max idle connections
- this number is unbounded (within the context of this template)
- the max number of connections per host is hardcoded to 100

The gorouter codebase does not put a bound on the max number of idle
connections. The value for `max_idle_connections` is given directly to
`http.Transport{MaxIdleConn:}`

Signed-off-by: Toby Lorne <527052641d65eef236eeef9545b2acac74c35d57@digital.cabinet-office.gov.uk>

cloudfoundry-incubator/cf-routing-release,cloudfoundry-incubator/cf-routing-release,cloudfoundry-incubator/cf-routing-release