Moved server socket deletion in 'process::finalize()'.
Moved server socket deletion in 'process::finalize()'.

We need to destroy the server socket and discard its
future before we finalize the process manager
because the socket's `onDiscard` callback may need to
run in the event loop (such as for libevent sockets), but
process manager finalization stops the event loop.

Review: https://reviews.apache.org/r/53975/

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