Add an test for QA::Runtime::RSAKey

qa/spec/runtime/rsa_key.rb

+describe QA::Runtime::RSAKey do
+  describe '#public_key' do
+    subject { described_class.new.public_key }
+
+    it 'generates a public RSA key' do
+      expect(subject).to match(/\Assh\-rsa AAAA[0-9A-Za-z+\/]+={0,3}\z/)
+    end
+  end
+end