Fixed issue in the att-mpls.py mininet script.
Fixed issue in the att-mpls.py mininet script.

Change-Id: I0b1d421ca95576cfaac874078242960c99773ae9

LorenzReinhart/ONOSnew,oplinkoms/onos,donNewtonAlpha/onos,packet-tracker/onos,mengmoya/onos,packet-tracker/onos,ravikumaran2015/ravikumaran201504,rvhub/onos,rvhub/onos,zsh2938/onos,donNewtonAlpha/onos,kkkane/ONOS,y-higuchi/onos,chenxiuyang/onos,jmiserez/onos,mengmoya/onos,kuangrewawa/onos,planoAccess/clonedONOS,ravikumaran2015/ravikumaran201504,sdnwiselab/onos,LorenzReinhart/ONOSnew,opennetworkinglab/onos,y-higuchi/onos,zsh2938/onos,osinstom/onos,sdnwiselab/onos,y-higuchi/onos,chinghanyu/onos,ravikumaran2015/ravikumaran201504,jmiserez/onos,kuujo/onos,castroflavio/onos,sonu283304/onos,chenxiuyang/onos,sdnwiselab/onos,donNewtonAlpha/onos,CNlukai/onos-gerrit-test,gkatsikas/onos,oplinkoms/onos,Shashikanth-Huawei/bmp,zsh2938/onos,CNlukai/onos-gerrit-test,y-higuchi/onos,y-higuchi/onos,opennetworkinglab/onos,gkatsikas/onos,jinlongliu/onos,kkkane/ONOS,gkatsikas/onos,kuujo/onos,oeeagle/onos,jmiserez/onos,donNewtonAlpha/onos,LorenzReinhart/ONOSnew,VinodKumarS-Huawei/ietf96yang,sdnwiselab/onos,gkatsikas/onos,chinghanyu/onos,oplinkoms/onos,opennetworkinglab/onos,kkkane/ONOS,kuujo/onos,lsinfo3/onos,oeeagle/onos,maheshraju-Huawei/actn,kuangrewawa/onos,rvhub/onos,castroflavio/onos,LorenzReinhart/ONOSnew,mengmoya/onos,Shashikanth-Huawei/bmp,maheshraju-Huawei/actn,zsh2938/onos,opennetworkinglab/onos,castroflavio/onos,castroflavio/onos,maheshraju-Huawei/actn,kuangrewawa/onos,maheshraju-Huawei/actn,Shashikanth-Huawei/bmp,lsinfo3/onos,mengmoya/onos,opennetworkinglab/onos,gkatsikas/onos,opennetworkinglab/onos,oeeagle/onos,mengmoya/onos,VinodKumarS-Huawei/ietf96yang,sdnwiselab/onos,gkatsikas/onos,oplinkoms/onos,planoAccess/clonedONOS,maheshraju-Huawei/actn,SmartInfrastructures/dreamer,donNewtonAlpha/onos,chinghanyu/onos,kuujo/onos,VinodKumarS-Huawei/ietf96yang,packet-tracker/onos,osinstom/onos,osinstom/onos,Shashikanth-Huawei/bmp,kuujo/onos,lsinfo3/onos,jinlongliu/onos,kkkane/ONOS,kuujo/onos,sonu283304/onos,oeeagle/onos,chenxiuyang/onos,SmartInfrastructures/dreamer,CNlukai/onos-gerrit-test,kuujo/onos,osinstom/onos,oplinkoms/onos,sonu283304/onos,sdnwiselab/onos,lsinfo3/onos,jinlongliu/onos,sonu283304/onos,VinodKumarS-Huawei/ietf96yang,CNlukai/onos-gerrit-test,Shashikanth-Huawei/bmp,chinghanyu/onos,rvhub/onos,LorenzReinhart/ONOSnew,osinstom/onos,jinlongliu/onos,oplinkoms/onos,jmiserez/onos,packet-tracker/onos,chenxiuyang/onos,VinodKumarS-Huawei/ietf96yang,planoAccess/clonedONOS,planoAccess/clonedONOS,SmartInfrastructures/dreamer,oplinkoms/onos