Fix ssh connections to IPv6 addresses

We can unconditionally wrap remote_addr in square brackets for scp and
sftp (both of which require them for IPv6 addresses), but not wrap them
at all for ssh (which doesn't accept them). This way, we don't have to
detect and treat IPv6 addresses specially. This works for hostnames,
IPv4 addresses, and IPv6 addresses.

The earlier code seemed to intend to wrap all IPv6 addresses in square
brackets, which would have broken ssh, but it actually made no attempt
to detect IPv6 addresses at all (so it broke only with IPv6 addresses
for scp and sftp).

Based on a review of PR #11677 by @JuiceBoxSingularity

lib/ansible/plugins/connections/ssh.py

@@ -57,11 +57,7 @@ class Connection(ConnectionBase):
 
         super(Connection, self).__init__(*args, **kwargs)
 
-        # FIXME: make this work, should be set from connection info
-        self._ipv6 = False
         self.host = self._play_context.remote_addr
-        if self._ipv6:
-            self.host = '[%s]' % self.host
 
     @property
     def transport(self):
@@ -342,8 +338,6 @@ class Connection(ConnectionBase):
             ssh_cmd.append("-q")
         ssh_cmd += self._common_args
 
-        if self._ipv6:
-            ssh_cmd += ['-6']
         ssh_cmd.append(self.host)
 
         ssh_cmd.append(cmd)
@@ -437,15 +431,19 @@ class Connection(ConnectionBase):
             raise AnsibleFileNotFound("file or module does not exist: {0}".format(in_path))
         cmd = self._password_cmd()
 
+        # scp and sftp require square brackets for IPv6 addresses, but
+        # accept them for hostnames and IPv4 addresses too.
+        host = '[%s]' % self.host
+
         if C.DEFAULT_SCP_IF_SSH:
             cmd.append('scp')
             cmd.extend(self._common_args)
-            cmd.extend([in_path, '{0}:{1}'.format(self.host, pipes.quote(out_path))])
+            cmd.extend([in_path, '{0}:{1}'.format(host, pipes.quote(out_path))])
             indata = None
         else:
             cmd.append('sftp')
             cmd.extend(self._common_args)
-            cmd.append(self.host)
+            cmd.append(host)
             indata = "put {0} {1}\n".format(pipes.quote(in_path), pipes.quote(out_path))
 
         (p, stdin) = self._run(cmd, indata)