Miscellaneous changes to capistrano deployment:

- use rvm1-capistrano3 gem instead of capistrano-rvm. It's supposed to be smarter knowing when to use rvm to launch a binary (e.g. bundler)

- fix error when setting pumactl to be launched with bundler (missing parentheses)

- run pumactl from the release path

- only the server in which Puma runs has the app role

put pumactl command definition, which is stage-specific, into the staging and production stage definitions, instead of the main deploy.rb file.