New property specifying username for user rbenv installs

* No longer can use path expansion within ENV since SSHKit quotes all
values as of capistrano/sshkit#250
* Only requires property be set if the install type is :user

README.md

@@ -29,6 +29,7 @@ And then execute:
 
     # config/deploy.rb
     set :rbenv_type, :user # or :system, depends on your rbenv setup
+    set :rbenv_user, 'username' # specify which user if rbenv_type is :user
     set :rbenv_ruby, '2.0.0-p247'
 
     # in case you want to set ruby version from the file:

lib/capistrano/tasks/rbenv.rake

@@ -30,14 +30,23 @@ Capistrano::DSL.stages.each do |stage|
   after stage, 'rbenv:map_bins'
 end
 
+module Capistrano
+  class RbenvError < StandardError
+  end
+end
+
 namespace :load do
   task :defaults do
     set :rbenv_path, -> {
       rbenv_path = fetch(:rbenv_custom_path)
       rbenv_path ||= if fetch(:rbenv_type, :user) == :system
         "/usr/local/rbenv"
       else
-        "~/.rbenv"
+        rbenv_user = fetch(:rbenv_user)
+        if rbenv_user.nil?
+          fail Capistrano::RbenvError, "rbenv: rbenv_user is not set"
+        end
+        "/home/#{rbenv_user}/.rbenv"
       end
     }