enable rpc service for devstacks

[estute]

Starting with Ficus (first devstack to run Xenial and therefore defaulting to use systemd for init), I have run into multiple FS locks when running tests (while locally running a host system running systemd).

@edx/devops I would like your opinion: Should this be something contained within the play, or instructions for Linux users? CC @benpatterson

[jibsheet]

This seems fine to me, but I would want to be sure from @nedbat and @gsong that it's either a no-op or a benefit for OS-X users.

[gsong]

@estute @jibsheet Is there some way to test this change on OS X/macOS?

[jibsheet]

@gsong I'd probably just take a normal ficus devstack running on an OS-X host and run the systemctl task his play does and then see if tests are better/worse. Stu can speak to which suites were breaking on him (python or bokchoy, I assume bokchoy).

[estute]

@gsong I was seeing this when running the bokchoy servers. Running "paver test_bokchoy --serversonly" was causing an fslock conflict