Add paramiko requirement for SSH transport

Signed-off-by: Joffrey F <joffrey@docker.com>

requirements.txt

@@ -9,6 +9,7 @@ enum34==1.1.6
 idna==2.5
 ipaddress==1.0.18
 packaging==16.8
+paramiko==2.4.2
 pycparser==2.17
 pyOpenSSL==18.0.0
 pyparsing==2.2.0

setup.py

@@ -42,6 +42,9 @@ extras_require = {
     # 'requests[security] >= 2.5.2, != 2.11.0, != 2.12.2'
     'tls': ['pyOpenSSL>=17.5.0', 'cryptography>=1.3.4', 'idna>=2.0.0'],
 
+    # Only required when connecting using the ssh:// protocol
+    'ssh': ['paramiko>=2.4.2'],
+
 }
 
 version = None