reboot: Fix typo and support bare Linux systems (#45607)

* reboot: Fix typo and support bare Linux systems

This fixes a problem for bare Linux systems that do not support 'who -b' or 'uptime -s'.

* Accumulate stdout and stderr information

(cherry picked from commit a7a99c5fd4)

changelogs/fragments/reboot-var-fix-bare-linux.yaml

@@ -0,0 +1,2 @@
+bugfixes:
+  - reboot - use correct syntax for fetching a value from a dict and account for bare Linux systems (https://github.com/ansible/ansible/pull/45607#issuecomment-422403177)

lib/ansible/plugins/action/reboot.py

@@ -94,6 +94,8 @@ class ActionModule(ActionBase):
         return reboot_command
 
     def get_system_boot_time(self):
+        stdout = ''
+        stderr = ''
         command_result = self._low_level_execute_command(self.DEFAULT_BOOT_TIME_COMMAND, sudoable=self.DEFAULT_SUDOABLE)
 
         # For single board computers, e.g., Raspberry Pi, that lack a real time clock and are using fake-hwclock
@@ -101,11 +103,22 @@ class ActionModule(ActionBase):
         # Fall back to using uptime -s for those systems.
         # https://github.com/systemd/systemd/issues/6057
         if '1970-01-01 00:00' in command_result['stdout']:
+            stdout += command_result['stdout']
+            stderr += command_result['stderr']
             command_result = self._low_level_execute_command('uptime -s', sudoable=self.DEFAULT_SUDOABLE)
 
+        # This is a last resort for bare Linux systems (e.g. OpenELEC) where 'who -b' or 'uptime -s' are not supported.
+        # Other options like parsing /proc/uptime or default uptime output are less reliable than this
         if command_result['rc'] != 0:
+            stdout += command_result['stdout']
+            stderr += command_result['stderr']
+            command_result = self._low_level_execute_command('cat /proc/sys/kernel/random/boot_id', sudoable=self.DEFAULT_SUDOABLE)
+
+        if command_result['rc'] != 0:
+            stdout += command_result['stdout']
+            stderr += command_result['stderr']
             raise AnsibleError("%s: failed to get host boot time info, rc: %d, stdout: %s, stderr: %s"
-                               % (self._task.action, command_result.rc, to_native(command_result['stdout']), to_native(command_result['stderr'])))
+                               % (self._task.action, command_result['rc'], to_native(stdout), to_native(stderr)))
 
         return command_result['stdout'].strip()