Handle SSH keys that have multiple spaces between each marker

Notice what happens when a user adds a key with a space in between:

```
irb(main):004:0> 'ssh-rsa  foobar'.split(/ /)
=> ["ssh-rsa", "", "foobar"]
```

This would cause gitlab-shell to receive a blank argument for the actual
key, leading to users unable to login.

1 files changed, 9 insertions, 0 deletions

diff --git a/spec/lib/gitlab/backend/shell_spec.rb b/spec/lib/gitlab/backend/shell_spec.rb
index 4b08a02ec73..6675d26734e 100644
--- a/spec/lib/gitlab/backend/shell_spec.rb
+++ b/spec/lib/gitlab/backend/shell_spec.rb
@@ -69,6 +69,15 @@ describe Gitlab::Shell, lib: true do
         expect(io).to have_received(:puts).with("key-42\tssh-rsa foo")
       end
 
+      it 'handles multiple spaces in the key' do
+        io = spy(:io)
+        adder = described_class.new(io)
+
+        adder.add_key('key-42', "ssh-rsa  foo")
+
+        expect(io).to have_received(:puts).with("key-42\tssh-rsa foo")
+      end
+
       it 'raises an exception if the key contains a tab' do
         expect do
           described_class.new(StringIO.new).add_key('key-42', "ssh-rsa\tfoobar")