Fix tempest logging configuration

This commit will correctly set the tempest output logging to dump
all of tempest logs into a tempest.log file in
$DEST/tempest/tempest.log. This will also fix the logging for
tempest in the gate so it will no longer print every log message on
the console.

Fixes bug 1207066

Change-Id: I91f2ee781c4a7a18c561ea3e3b26832b97431464
Merge "Fix tempest logging configuration"