Updated post-reviews to catch exceptions and return None if ignoring errors in execute.
Updated post-reviews to catch exceptions and return None if ignoring
errors in execute.

Review: https://reviews.apache.org/r/21086

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