Fix conditional for docker prebuilt option
Fix conditional for docker prebuilt option

In an earlier version of docker module.mk
the value "false" was used instead of "0"
to mean false, but was incorrectly updated.

blueprint fuel-containerization-of-services

Change-Id: I67aead2999248738a5ce6efac82e5cd3cf36f797

zhaochao/fuel-main,dancn/fuel-main-dev,Fiware/ops.Fuel-main-dev,stackforge/fuel-main,teselkin/fuel-main,Fiware/ops.Fuel-main-dev,eayunstack/fuel-main,huntxu/fuel-main,SergK/fuel-main,eayunstack/fuel-main,huntxu/fuel-main,AnselZhangGit/fuel-main,dancn/fuel-main-dev,SmartInfrastructures/fuel-main-dev,SmartInfrastructures/fuel-main-dev,stackforge/fuel-main,SergK/fuel-main,huntxu/fuel-main,teselkin/fuel-main,zhaochao/fuel-main,SmartInfrastructures/fuel-main-dev,AnselZhangGit/fuel-main,Fiware/ops.Fuel-main-dev,dancn/fuel-main-dev,ddepaoli3/fuel-main-dev,Fiware/ops.Fuel-main-dev,AnselZhangGit/fuel-main,zhaochao/fuel-main,ddepaoli3/fuel-main-dev,eayunstack/fuel-main,teselkin/fuel-main,ddepaoli3/fuel-main-dev,SmartInfrastructures/fuel-main-dev,AnselZhangGit/fuel-main,dancn/fuel-main-dev,stackforge/fuel-main,zhaochao/fuel-main,zhaochao/fuel-main,teselkin/fuel-main,ddepaoli3/fuel-main-dev,SergK/fuel-main