[BUILD] Fixes dependency issue with log4j in IntelliJ

IDEA provides its own log4j library, but there are
classloader errors when that one is used. Setting our log4j
library's scope to "Provided" makes sure that it is used at
runtime.

Change-Id: I848b6ae179df6e329556d9eeea2fa8dc9229226f
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/2011
Tested-by: Jenkins CI
Reviewed-by: Matthias Bohnstedt <matthias.bohnstedt@gmail.com>
Reviewed-by: Damla Durmaz <ddurmaz88@gmail.com>
Reviewed-by: Holger Schmeisky <google@schmeisky.com>