Normalize space-like characters in keys before output to gitlab-shell

gitlab-shell expects only one tab separator per key, and an SSH key with
a tab character in the comment, for example, would break things.

Closes #2970

lib/gitlab/backend/shell.rb

@@ -4,7 +4,8 @@ module Gitlab
 
     class KeyAdder < Struct.new(:io)
       def add_key(id, key)
-        io.puts("#{id}\t#{key.strip}")
+        key.gsub!(/[[:space:]]+/, ' ').strip!
+        io.puts("#{id}\t#{key}")
       end
     end
 

spec/lib/gitlab/backend/shell_spec.rb

@@ -15,4 +15,17 @@ describe Gitlab::Shell do
   it { is_expected.to respond_to :fork_repository }
 
   it { expect(gitlab_shell.url_to_repo('diaspora')).to eq(Gitlab.config.gitlab_shell.ssh_path_prefix + "diaspora.git") }
+
+  describe Gitlab::Shell::KeyAdder do
+    describe '#add_key' do
+      it 'normalizes space characters in the key' do
+        io = spy
+        adder = described_class.new(io)
+
+        adder.add_key('key-42', "sha-rsa foo\tbar\tbaz")
+
+        expect(io).to have_received(:puts).with("key-42\tsha-rsa foo bar baz")
+      end
+    end
+  end
 end