Frontend disables keepalive for Chrome on OSX

The frontend disables keepalive for Chrome on OSX, which I just noticed. You can test it yourself via:

```
curl -v -s -o /dev/null -k --key /tmp/x509up_u112870 --cert /tmp/x509up_u112870 'https://cmsweb.cern.ch/' -H "Connection: keep-alive"

curl -v -s -o /dev/null -k --key /tmp/x509up_u112870 --cert /tmp/x509up_u112870 'https://cmsweb.cern.ch/' -H "Connection: keep-alive" -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.116 Safari/537.36'
```

These yield:

```
No user-agent:
> GET / HTTP/1.1
> Host: cmsweb.cern.ch
> Accept: */*
> Connection: keep-alive

**snip**

< HTTP/1.1 200 OK
< Date: Tue, 01 Mar 2016 17:33:51 GMT
< Server: Apache
< Last-Modified: Mon, 25 Jan 2016 14:49:41 GMT
< ETag: "8d7-52a29adc5cb40"
< Accept-Ranges: bytes
< Content-Length: 2263
< CMS-Server-Time: D=678 t=1456853631811320
< Keep-Alive: timeout=5, max=100
< Connection: Keep-Alive

Chrome user-agent:
> GET / HTTP/1.1
> Host: cmsweb.cern.ch
> Accept: */*
> Connection: keep-alive
> User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.116 Safari/537.36

**snip**

< HTTP/1.1 200 OK
< Date: Tue, 01 Mar 2016 17:33:58 GMT
< Server: Apache
< Last-Modified: Mon, 25 Jan 2016 14:49:41 GMT
< ETag: "8d7-52a29adc5cb40"
< Accept-Ranges: bytes
< Content-Length: 2263
< CMS-Server-Time: D=1290 t=1456853638447423
< Connection: close
```

This appears to be related to the following line https://github.com/dmwm/deployment/blob/dfb5840480c6477a899e6fb2ff39af84ed49a560/frontend/frontend.conf#L1 which matches against `Safari` in Chrome's user-agent of `User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.116 Safari/537.36`

A simple solution would be to add `BrowserMatch Chrome !nokeepalive` to the subsequent line, though it's not clear that would do 100% the right thing. I'd test it myself, but my dev frontend on my machine isn't cooperating right now :frowning:. It'd be neat (?) to get a list of unique user-agents to work with. That'd help figure out the right matches needed.