[core] Breaks down rake tasks

While documenting our release process, we can see some things that don't
need to be locked together are.

This splits release into prepare/publish parts

Now anyone can prepare a release but will not be able to publish that
release without the correct access to Github and Rubygems.

Adds a preflight task and adds a check for existing tags to that.

RELEASE.md

@@ -23,13 +23,13 @@ services)
 * Update the version number (`lib/fog/version.rb`)
 * Run `rake changelog` to update `changelog.txt`
 * Run `rake release` to prepare the release which does:
-  * Builds the gem (`rake build`)
-  * Tags the commit
-  * Creates commits for version and pushes to github (Requires
-Credentials)
-  * Pushes gem to rubygems (Requires Credentials)
-  * Creates site documentation (`rake docs`)
-  * Pushes site documentation to S3 (Requires Credentials)
+  * Prepares the release (`rake release:prepare`)
+    * Builds the gem
+    * Tags the commit
+    * Creates commits for version
+  * Publishes the release (`rake release:publish`)
+    * Pushes commit and tag to Github (Requires Credentials)
+    * Pushes gem to Rubygems (Requires Credentials)
 
 ## Announce the release
 

Rakefile

@@ -95,16 +95,43 @@ end
 #
 #############################################################################
 
-task :release => :build do
-  unless `git branch` =~ /^\* master$/
-    puts "You must be on the master branch to release!"
-    exit!
+task :release => ["release:prepare", "release:publish"]
+
+namespace :release do
+  task :preflight do
+    unless `git branch` =~ /^\* master$/
+      puts "You must be on the master branch to release!"
+      exit!
+    end
+    if `git tag` =~ /^\* v#{version}$/
+      puts "Tag v#{version} already exists!"
+      exit!
+    end
   end
-  sh "gem install pkg/#{name}-#{version}.gem"
+
+  task :prepare => :preflight do
+    Rake::Task[:build].invoke
+    sh "gem install pkg/#{name}-#{version}.gem"
+    Rake::Task[:git_mark_release].invoke
+  end
+
+  task :publish do
+    Rake::Task[:git_push_release].invoke
+    Rake::Task[:gem_push].invoke
+  end
+end
+
+task :git_mark_release do
   sh "git commit --allow-empty -a -m 'Release #{version}'"
   sh "git tag v#{version}"
+end
+
+task :git_push_release do
   sh "git push origin master"
   sh "git push origin v#{version}"
+end
+
+task :gem_push do
   sh "gem push pkg/#{name}-#{version}.gem"
 end