GUI: Better error messages for minify task in gulp
GUI: Better error messages for minify task in gulp

Change-Id: I25f287ae057ea8f164c5ec7a3f036f3e92dd8f3c

gkatsikas/onos,kuujo/onos,gkatsikas/onos,kuujo/onos,opennetworkinglab/onos,oplinkoms/onos,oplinkoms/onos,LorenzReinhart/ONOSnew,oplinkoms/onos,oplinkoms/onos,oplinkoms/onos,opennetworkinglab/onos,kuujo/onos,oplinkoms/onos,osinstom/onos,gkatsikas/onos,opennetworkinglab/onos,osinstom/onos,LorenzReinhart/ONOSnew,opennetworkinglab/onos,gkatsikas/onos,LorenzReinhart/ONOSnew,kuujo/onos,LorenzReinhart/ONOSnew,osinstom/onos,osinstom/onos,oplinkoms/onos,kuujo/onos,osinstom/onos,gkatsikas/onos,kuujo/onos,opennetworkinglab/onos,gkatsikas/onos,kuujo/onos,opennetworkinglab/onos,LorenzReinhart/ONOSnew