Do not fail if /proc/uptime is not present

This can happen in chroot environments that don't have all of /proc
available

lib/ansible/module_utils/facts.py

@@ -1089,7 +1089,9 @@ class LinuxHardware(Hardware):
             self.facts['devices'][diskname] = d
 
     def get_uptime_facts(self):
-        uptime_seconds_string = get_file_content('/proc/uptime').split(' ')[0]
+        uptime_file_content = get_file_content('/proc/uptime')
+        if uptime_file_content:
+            uptime_seconds_string = uptime_file_content.split(' ')[0]
             self.facts['uptime_seconds'] = int(float(uptime_seconds_string))
 
     def get_lvm_facts(self):