SDN check: Ignore errors from `oc version`

Ignore the exit code from executing `oc version`, and capture any error
output.

On containerized nodes, the oc executable may not exist, in which case the
check should not fail but should instead merely log the "command not found"
error.

This commit is a follow-up to commit d2a8a34392f866b62a98eaddf8dd6fbe57d72ee6.

This commit fixes bug 1615705.

https://bugzilla.redhat.com/show_bug.cgi?id=1615705#c1

* roles/openshift_health_checker/openshift_checks/sdn.py (SDNCheck.run):
Ignore exit code from oc version check and capture error output.

roles/openshift_health_checker/openshift_checks/sdn.py

@@ -61,8 +61,11 @@ class SDNCheck(OpenShiftCheck):
                 oc_executable = self.get_var('openshift_client_binary',
                                              default='/bin/oc')
                 oc_executable = self.template_var(oc_executable)
-                self.save_command_output('oc-version', [oc_executable,
-                                                        'version'])
+                # The oc executable is not installed on containerized nodes, so
+                # use "2>&1" to capture any error output (such as "command not
+                # found"), and use "|| :" to ignore the exit code.
+                self.save_command_output('oc-version',
+                                         oc_executable + ' version 2>&1 || :')
                 self.register_file('os-version', None,
                                    '/etc/system-release-cpe')
             except OpenShiftCheckException as exc: