Log correctly encoded url with parameters for nginx

$uri uses \x escaping instead of % and does not contain the request
parameters. So we switch to $request_uri, which escapes using %, and
contains the request parameters. Thereby we lessen impact of bug 58316
and directly address bug 58876.

Bug: 58876
Change-Id: I400932069e993fce13c20ea039eb0f022cea83bf
Stop nginx from escaping the user agent

Nginx still escaped spaces in user agents. Since we switched to tabs
as separators, escaping (which mostly affected spaces) is more in the
way than it helps. Hence, we drop the escaping to match output we see
from varnish.

If user agents come with tabs, tabs are not escaped and the log line
columns after the user agent column shift further back. While that's
not ideal, we have the same problem for Varnish log lines --- and it
effectively does not affect us. So we prefer to have user agents
uniformly presented, even if it potentiall breaks a log line in corner
cases.

Change-Id: Ia8933d30a0672b6fe902ce698b17b578c1a27547