Cleaned up the health check launcher code in docker executor.
Cleaned up the health check launcher code in docker executor.

This change cleans up the code a bit making it easier to read:

- Bail out early wherever possible to reduce nestedness of code
making it easier to read.
- Minor cleanups around merging conditions together wherever
possible.

Review: https://reviews.apache.org/r/45557/

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