Update agent proxy-user plugin for apache format

[jaehong-kim]

Update agent proxy-user plugin for apache format

Apache %t, %D format.

%t: The time the request was received in Universal Coordinated Time since the epoch (Jan. 1, 1970) measured in microseconds. The value is preceded by t=.
%D: The time from when the request was received to the time the headers are sent on the wire. This is a measure of the duration of the request. The value is preceded by D=. The value is measured in microseconds.

Apache HTTP Server

• http://httpd.apache.org/docs/2.4/en/mod/mod_headers.html

Add HTTP header.

X-ApacheLB: t=991424704447256 D=3775428

e.g.

httpd.conf

<IfModule mod_jk.c>
...
RequestHeader set X-ApacheLB "%t %D"
...
</IfModule>

%t is required value.

[jaehong-kim]