Set ruby stack size env variables in worker_ctl
Set ruby stack size env variables in worker_ctl

This change updates `RUBY_THREAD_MACHINE_STACK_SIZE` and
`RUBY_THREAD_VM_STACK_SIZE` to 16 MB. This allows the bosh workers to
allocate a large number of static ips (250+). Previously, when these
were unset, the workers would error for `stack level too deep`.

[#159494222](https://www.pivotaltracker.com/story/show/159494222)

Co-authored-by: Belinda Liu <496afffef642eb3807bf00ef2898c80e8c6b937c@pivotal.io>

barthy1/bosh,barthy1/bosh,barthy1/bosh,barthy1/bosh