Avoid 'using namespace' clause in the test containerizer.
Avoid 'using namespace' clause in the test containerizer.

Review: https://reviews.apache.org/r/53456

neilconway/mesos,chhsia0/mesos,zmalik/mesos,Aman-Jain-14/customizedMesos,Gilbert88/mesos,gsantovena/mesos,neilconway/mesos,asamerh4/mesos,yuquanshan/customizedMesos,yuquanshan/customizedMesos,chhsia0/mesos,verizonlabs/mesos,andschwa/mesos,zmalik/mesos,chhsia0/mesos,kaysoky/mesos,abudnik/mesos,jpeach/mesos,jpeach/mesos,abudnik/mesos,verizonlabs/mesos,reneploetz/mesos,asamerh4/mesos,zmalik/mesos,Aman-Jain-14/customizedMesos,andschwa/mesos,Gilbert88/mesos,craimbert/mesos,zmalik/mesos,asamerh4/mesos,jpeach/mesos,zmalik/mesos,chhsia0/mesos,Aman-Jain-14/customizedMesos,craimbert/mesos,reneploetz/mesos,andschwa/mesos,neilconway/mesos,Gilbert88/mesos,jpeach/mesos,andschwa/mesos,yuquanshan/customizedMesos,asamerh4/mesos,kaysoky/mesos,abudnik/mesos,andschwa/mesos,kaysoky/mesos,asamerh4/mesos,reneploetz/mesos,dforsyth/mesos,yuquanshan/customizedMesos,abudnik/mesos,chhsia0/mesos,neilconway/mesos,kaysoky/mesos,verizonlabs/mesos,kaysoky/mesos,dforsyth/mesos,verizonlabs/mesos,neilconway/mesos,gsantovena/mesos,craimbert/mesos,asamerh4/mesos,dforsyth/mesos,Aman-Jain-14/customizedMesos,zmalik/mesos,andschwa/mesos,Gilbert88/mesos,verizonlabs/mesos,chhsia0/mesos,dforsyth/mesos,reneploetz/mesos,dforsyth/mesos,neilconway/mesos,gsantovena/mesos,jpeach/mesos,gsantovena/mesos,kaysoky/mesos,craimbert/mesos,andschwa/mesos,gsantovena/mesos,jpeach/mesos,craimbert/mesos,zmalik/mesos,Aman-Jain-14/customizedMesos,Gilbert88/mesos,yuquanshan/customizedMesos,craimbert/mesos,verizonlabs/mesos,reneploetz/mesos,asamerh4/mesos,Aman-Jain-14/customizedMesos,dforsyth/mesos,abudnik/mesos,Gilbert88/mesos,kaysoky/mesos,abudnik/mesos,gsantovena/mesos,Gilbert88/mesos,reneploetz/mesos,verizonlabs/mesos,neilconway/mesos,abudnik/mesos,gsantovena/mesos,reneploetz/mesos,yuquanshan/customizedMesos,jpeach/mesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos,dforsyth/mesos,chhsia0/mesos,craimbert/mesos