Use Tempfile instead of `sed -i`

The syntax for `sed -i` is incompatible between GNU sed and
BSD sed. By Tempfile from the Ruby standard library we can
avoid using the `-i` option of sed.

lib/gitlab_keys.rb

+require 'tempfile'
 
 require_relative 'gitlab_config'
 require_relative 'gitlab_logger'
@@ -35,9 +36,11 @@ class GitlabKeys
 
   def rm_key
     $logger.info "Removing key #{@key_id}"
-    cmd = "sed -i '/shell #{@key_id}\"/d' #{auth_file}"
+    Tempfile.open('authorized_keys') do |temp|
+      cmd = "sed '/shell #{@key_id}\"/d' #{auth_file} > #{temp.path} && mv #{temp.path} #{auth_file}"
       system(cmd)
     end
+  end
 
   def clear
     system("echo '# Managed by gitlab-shell' > #{auth_file}")

spec/gitlab_keys_spec.rb

@@ -31,9 +31,12 @@ describe GitlabKeys do
 
   describe :rm_key do
     let(:gitlab_keys) { build_gitlab_keys('rm-key', 'key-741', 'ssh-rsa AAAAB3NzaDAxx2E') }
+    let(:temp_file) { mock(:temp_file, path: 'tmp_path') }
+    before { Tempfile.should_receive(:open).and_yield(temp_file) }
 
     it "should receive valid cmd" do
-      valid_cmd = "sed -i '/shell key-741\"/d' #{GitlabConfig.new.auth_file}"
+      auth_file = GitlabConfig.new.auth_file
+      valid_cmd = "sed '/shell key-741\"/d' #{auth_file} > tmp_path && mv tmp_path #{auth_file}"
       gitlab_keys.should_receive(:system).with(valid_cmd)
       gitlab_keys.send :rm_key
     end