Replace cat with Ruby's read_file

Thanks to wvu-r7 for the comment

Author: jvoisin

modules/exploits/linux/local/netfilter_priv_esc.rb

@@ -67,15 +67,15 @@ def iptables_loaded?()
       # x_tables 36864 2 iptable_filter,ip_tables, Live 0x0000000000000000
       vprint_status('Checking if ip_tables is loaded in kernel')
       if target.name == "Ubuntu"
-        iptables = cmd_exec('cat /proc/modules')
+        iptables = read_file('/proc/modules')
         if iptables.include?('ip_tables')
           vprint_good('ip_tables.ko is loaded')
         else
           print_error('ip_tables.ko is not loaded.  root needs to run iptables -L or similar command')
         end
         return iptables.include?('ip_tables')
       elsif target.name == "Fedora"
-        iptables = cmd_exec('cat /proc/modules')
+        iptables = read_file('/proc/modules')
         if iptables.include?('iptable_raw')
           vprint_good('iptable_raw is loaded')
         else