Connection error messages are unsafe: wrap them (#37329)

* Check that connection error msg are not unsafe

* Connection error messages are unsafe: wrap them

For example, in case of error, docker connection plugin returns exception
message containing Go template. These messages weren't tagged as unsafe
and were consequently rendered:

The conditional check 'result is failed' failed. The error was:
{
  'msg': u'Docker version check ([\'/usr/bin/docker\', \'version\', \'--format\', "\'{{.Server.Version}}\'"]) failed: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.35/version: dial unix /var/run/docker.sock: connect: permission denied\n',
  'failed': True
}:
template error while templating string: unexpected '.'.
String: Docker version check (['/usr/bin/docker', 'version', '--format', "'{{.Server.Version}}'"]) failed: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.35/version: dial unix /var/run/docker.sock: connect: permission denied

test/integration/targets/connection/inventory

@@ -0,0 +1,2 @@
+[local]
+testhost