Testing with remote server cache is unusably slow

Testing with remote server cache is unusably slow
https://bugs.webkit.org/show_bug.cgi?id=153928

Reviewed by Chris Dumez.

Don't use the single process mode of httpd as it's way too slow even for testing.
Also we'll hit a null pointer crash (http://svn.apache.org/viewvc?view=revision&revision=1711479)

Since httpd exits immediately when launched in multi-process mode, remote-cache-server.py (renamed from
run-with-remote-server.py) now has "start" and "stop" commands to start/stop the Apache. Also added
"reset" command to reset the cache for convenience.

* Install.md: Updated the instruction.
* config.json: Fixed a typo: httpdErro*r*Log.
* tools/remote-cache-server.py: Copied from Websites/perf.webkit.org/tools/run-with-remote-server.py.
Now takes one of the following commands: "start", "stop", and "reset".
(main):
(start_httpd): Extracted from main.
(stop_httpd): Added.
* tools/remote-server-relay.conf: Removed redundant (duplicate) LoadModule's.
* tools/run-with-remote-server.py: Removed.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@196195 268f45cc-cd09-0410-ab3c-d52691b4dbfc