Updated 'HealthCheck' protobuf validation in docker executor.
Updated 'HealthCheck' protobuf validation in docker executor.

Review: https://reviews.apache.org/r/51039/

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