Updated CHANGELOG with fetcher user changes.
Updated CHANGELOG with fetcher user changes.

The fetcher was changed to assume the same user as a task when fetching
files. This patch updates the CHANGELOG accordingly.

Review: https://reviews.apache.org/r/50283/

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