Add support for the SSH ControlPath connection sharing option

OpenSSH multiplexing needs 3 configuration items:
* ControlPath
* ControlMaster
* ControlPersist

Testinfra just uses the last two and this causes that multiplexing is not used:

```
DEBUG    testinfra:base.py:288 RUN CommandResult(command=b'ssh -o ControlMaster=auto -o ControlPersist=1200 -o ServerAliveInterval=180 -o StrictHostKeyChecking=no -o User=<reducted> -i \'~/.ssh/<reducted>\' -o ConnectTimeout=10 <reducted> \'sudo /bin/sh -c \'"\'"\'<reducted>\'"\'"\'\'', exit_status=0, stdout=b'<reducted>', stderr=None)
```

In comparison, Ansible uses all 3 parameters:

```
SSH: EXEC ssh -o ControlMaster=auto -o ControlPersist=1200 -o ServerAliveInterval=180 -o StrictHostKeyChecking=no -o StrictHostKeyChecking=no -o 'IdentityFile="<reducted>"' -o KbdInteractiveAuthentication=no -o PreferredAuthentications=gssapi-with-mic,gssapi-keyex,hostbased,publickey -o PasswordAuthentication=no -o 'User="<reducted>"' -o ConnectTimeout=10 -o 'ControlPath="<reducted>/.ansible/cp/%C"' <reducted>
```

With this change the third option to control connection sharing is introduced.

testinfra/backend/ssh.py

@@ -26,6 +26,7 @@ def __init__(
         ssh_config=None,
         ssh_identity_file=None,
         timeout=10,
+        controlpath="",
         controlpersist=60,
         ssh_extra_args=None,
         *args,
@@ -35,6 +36,7 @@ def __init__(
         self.ssh_config = ssh_config
         self.ssh_identity_file = ssh_identity_file
         self.timeout = int(timeout)
+        self.controlpath = controlpath
         self.controlpersist = int(controlpersist)
         self.ssh_extra_args = ssh_extra_args
         super().__init__(self.host.name, *args, **kwargs)
@@ -74,6 +76,12 @@ def _build_ssh_command(self, command):
                     self.controlpersist
                 )
             )
+        if (
+            "ControlMaster" in " ".join(cmd)
+            and self.controlpath
+            and ("controlpath" not in (self.ssh_extra_args or "").lower())
+        ):
+            cmd.append("-o ControlPath={}".format(self.controlpath))
         cmd.append("%s %s")
         cmd_args.extend([self.host.name, command])
         return cmd, cmd_args

testinfra/utils/ansible_runner.py

@@ -170,6 +170,16 @@ def get_config(name, default=None):
         ]
     ).strip()
 
+    control_path = config.get("ssh_connection", "control_path", fallback="", raw=True)
+    if control_path:
+        directory = config.get(
+            "persistent_connection", "control_path_dir", fallback="~/.ansible/cp"
+        )
+        control_path = control_path % ({"directory": directory})  # noqa: S001
+        # restore original "%%"
+        control_path = control_path.replace("%", "%%")
+        kwargs["controlpath"] = control_path
+
     spec = "{}://".format(connection)
 
     # Fallback to user:password auth when identity file is not used