check file exists before reading

Author: h00die

modules/post/linux/gather/mount_cifs_creds.rb

@@ -38,6 +38,7 @@ def run
     ])
 
     # parse each line from /etc/fstab
+    fail_with(Failure::NotFound, '/etc/fstab not found on system') unless file_exist?('/etc/fstab')
     read_file("/etc/fstab").each_line do |fstab_line|
       fstab_line.strip!
       # where we'll store the current parsed credentials, if any