Merge pull request #2608 in SNORT/snort3 from ~SHRARANG/snort3:lua_sandbox to master

Merge pull request #2608 in SNORT/snort3 from ~SHRARANG/snort3:lua_sandbox to master

Squashed commit of the following:

commit bd0c2a888b69a9791bb2b8dd196c8a6fdd53ca1c
Author: Shravan Rangaraju <shrarang@cisco.com>
Date:   Fri Jul 31 12:05:26 2020 -0400

    shell: support for loading configuration in lua sandbox

    Load snort configuration in a Lua sandbox. Sandbox configuration file can be specified
    with the command line option "--lua-sandbox". Snort expects this file to contain a Lua
    table named sandbox_env. sandbox_env should specify a list of allowed Lua functions.
    This table is used as the sandbox environment. Snort loads the following in the sandbox:
     - top-level configuration file specified by command line option "-c"
     - subpolicy files
     - all of the included files in above files and also files included in the included files
     - configuration overrides specified with command line option "--lua"
    If any of the above use Lua functionality not allowed in sandbox_env, snort will exit with
    a fatal error.