[LOG] changed logging files

All logging statements will now be written into the same file.

Reduced Log-Level for normal operation to INFO.

Changed the location of the log files. The log files can now be found in
$WORKSPACE/.metadata/.plugins/$SarosPluginID/log

Change-Id: Id09ba6b137103554ae55d72c53d46d8c45a2792f
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1996
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>