Updated changelog for 0.22.0.
Updated changelog for 0.22.0.

Review: https://reviews.apache.org/r/31324

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