Change httpd Keystone log level to default

Having Keystone's log level at debug caused a lot of uninteresting
Httpd-related log lines to be displayed which makes debugging more
difficult than it should be.

Rather than set the log level explicitly, Keystone will use the
Httpd server's setting, which defaults to warn.

Partial-Bug: #1359995
Change-Id: Ieef882944bafd98f7b27497a5276124b21c3e576
Merge "Change httpd Keystone log level to default"