ec2: add support for creation and importing of real SSH keys (#2108)

* ec2: add support for creation and importing of real SSH keys

* setup: lock PyYAML version to avoid incompatibilities

tests/test_ec2/helpers.py

@@ -0,0 +1,15 @@
+import six
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.primitives.asymmetric import rsa
+
+
+def rsa_check_private_key(private_key_material):
+    assert isinstance(private_key_material, six.string_types)
+
+    private_key = serialization.load_pem_private_key(
+        data=private_key_material.encode('ascii'),
+        backend=default_backend(),
+        password=None)
+    assert isinstance(private_key, rsa.RSAPrivateKey)