Avoid parallel builder tests creating cache dir
Avoid parallel builder tests creating cache dir

Running tests in parallel on fresh systems may result in more than one
test attempting to create the cache dir. Mock the CacheStorage object
for such tests to prevent this from happening.

Change-Id: I532fcceba86baad2d4669274e314cee21b78efa6

lukas-bednar/jenkins-job-builder,stanchan/jenkins-job-builder,dataxu/jenkins-job-builder,puppetlabs/jenkins-job-builder,stanchan/jenkins-job-builder,madAndroid/jenkins-job-builder,gforcada/jenkins-job-builder,simzacks/jjb,joostvdg/jenkins-job-builder,dataxu/jenkins-job-builder,phinexus/jenkins-job-builder,onshape/jenkins-job-builder,rsig/jenkins-job-builder,gforcada/jenkins-job-builder,wsoula/jenkins-job-builder,joostvdg/jenkins-job-builder,sunyi00/jenkins-job-builder,wikimedia/integration-jenkins-job-builder,gregsymons/jenkins-job-builder,CruGlobal/jenkins-job-builder,sebbrandt87/jenkins-job-builder,klmitch/jenkins-job-builder,gforcada/jenkins-job-builder,tamac-io/jenkins-job-builder,theforeman/jenkins-job-builder,gforcada/jenkins-job-builder,wikimedia/integration-jenkins-job-builder,sunyi00/jenkins-job-builder,CruGlobal/jenkins-job-builder,wsoula/jenkins-job-builder,lukas-bednar/jenkins-job-builder,tya/jenkins-job-builder,fuglu/jenkins-job-builder,madAndroid/jenkins-job-builder,twc-openstack/jenkins-job-builder,grdryn/jenkins-job-builder,phinexus/jenkins-job-builder,theforeman/jenkins-job-builder,klmitch/jenkins-job-builder,tya/jenkins-job-builder,dataxu/jenkins-job-builder,tya/jenkins-job-builder,david-caro/jenkins-job-builder,stanchan/jenkins-job-builder,grdryn/jenkins-job-builder,grdryn/jenkins-job-builder,sebbrandt87/jenkins-job-builder,twc-openstack/jenkins-job-builder,simzacks/jjb,rsig/jenkins-job-builder,jenshnielsen/jenkins-job-builder,puppetlabs/jenkins-job-builder,CruGlobal/jenkins-job-builder,simzacks/jjb,OSSystems/jenkins-job-builder,gregsymons/jenkins-job-builder,electrical/jenkins-job-builder,OSSystems/jenkins-job-builder,wsoula/jenkins-job-builder,pyatil/jenkins-job-builder,joostvdg/jenkins-job-builder,wikimedia/integration-jenkins-job-builder,tamac-io/jenkins-job-builder,mjeanson/jenkins-job-builder,mjeanson/jenkins-job-builder,linuxmaniac/jenkins-job-builder,jenshnielsen/jenkins-job-builder,puppetlabs/jenkins-job-builder,OSSystems/jenkins-job-builder,gregsymons/jenkins-job-builder,OSSystems/jenkins-job-builder,wikimedia/integration-jenkins-job-builder,vredchenko/jenkins-job-builder,tamac-io/jenkins-job-builder,madAndroid/jenkins-job-builder,GoodgameStudios/jenkins-job-builder,theforeman/jenkins-job-builder,linuxmaniac/jenkins-job-builder,pyatil/jenkins-job-builder,phinexus/jenkins-job-builder,sunyi00/jenkins-job-builder,linuxmaniac/jenkins-job-builder,pyatil/jenkins-job-builder,onshape/jenkins-job-builder,puppetlabs/jenkins-job-builder,lukas-bednar/jenkins-job-builder,pyatil/jenkins-job-builder,vredchenko/jenkins-job-builder,simzacks/jjb,linuxmaniac/jenkins-job-builder,joostvdg/jenkins-job-builder,twc-openstack/jenkins-job-builder,wsoula/jenkins-job-builder,fuglu/jenkins-job-builder,electrical/jenkins-job-builder,sebbrandt87/jenkins-job-builder,electrical/jenkins-job-builder,GoodgameStudios/jenkins-job-builder,vredchenko/jenkins-job-builder,onshape/jenkins-job-builder,klmitch/jenkins-job-builder,klmitch/jenkins-job-builder,mjeanson/jenkins-job-builder,lukas-bednar/jenkins-job-builder,david-caro/jenkins-job-builder,phinexus/jenkins-job-builder,tamac-io/jenkins-job-builder,rsig/jenkins-job-builder,jenshnielsen/jenkins-job-builder,dataxu/jenkins-job-builder,david-caro/jenkins-job-builder,wikimedia/integration-jenkins-job-builder,GoodgameStudios/jenkins-job-builder,rsig/jenkins-job-builder,fuglu/jenkins-job-builder,theforeman/jenkins-job-builder,david-caro/jenkins-job-builder,onshape/jenkins-job-builder,phinexus/jenkins-job-builder,gforcada/jenkins-job-builder,twc-openstack/jenkins-job-builder,mjeanson/jenkins-job-builder