move gem_home configuration for delayed_jobs to config folder

right now, the documentation tells people to change script/canvas_init, which
kinda sucks for people hoping to upgrade by doing git pull.

this seems sort of hacky - i'm open to suggestions.

Change-Id: I66bf3deb2f51c22c23c1963369c6ab3e5f391d33
Reviewed-on: https://gerrit.instructure.com/2145
Reviewed-by: Brian Palmer <brianp@instructure.com>
Tested-by: Hudson <hudson@instructure.com>

.gitignore

@@ -21,6 +21,7 @@ config/domain.yml
 config/etherpad.yml
 config/facebooker.yml
 config/file_store.yml
+config/GEM_HOME
 config/google_docs.yml
 config/kaltura.yml
 config/linked_in.yml

script/canvas_init

@@ -9,6 +9,8 @@
 # Short-Description:	Start/stop Canvas background jobs
 ### END INIT INFO
 
+set -e
+
 # drop privs if necessary
 if [ "$(id -u)" == "0" ]; then
   exec su $(stat -c %U $(dirname $(readlink -f $0))/../config/environment.rb) -- $0 $@
@@ -19,6 +21,9 @@ fi
 cd $(dirname $(readlink -f $0))/..
 
 # set up config
+if [ -e "config/GEM_HOME" ]; then
+  export GEM_HOME=$(cat config/GEM_HOME)
+fi
 #export GEM_HOME=/path/to/gem/home
 export RAILS_ENV=production