Added CHANGELOG description for reservation labels.
Added CHANGELOG description for reservation labels.

Review: https://reviews.apache.org/r/44371/

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