Used std::thread instead of pthread for ns tests.
Used std::thread instead of pthread for ns tests.

Review: https://reviews.apache.org/r/36824

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