New http pull methode

[Bierchermuesli]

I would like contribute another way for deploying large prefix lists. Instead of pushing the configuration, the prefix set can be pulled from the router itself like:

• copy http://203.0.113.1/pfxgen/42 running-config (default syntax)
• or
• copy http://203.0.113.1/pfxgen/iosxr/42 running-config

On the management station where irrpt is running, a working http server is nessessary. Sample nginx config:

   rewrite ^/pfxgen/(.*)$ /irrpt_pfxgen_http.php?$1 last;
   location ~ irrpt_pfxgen_http.php$ {
      include snippets/fastcgi-php.conf;
      root /opt/irrpt/bin;
      # With php-fpm:
      fastcgi_pass unix:/run/php/php-fpm.sock;
   }

The prefix lists can also be testen from any client (or monitoring systems) like

curl http://217.11.222.212/pfxgen/iosxr/42
! Generate for iosxr for ASN15576
prefix-set PS-IPV4-AS15576
  63.246.32.0/20 le 32,
  65.22.19.0/24 le 32,
etc..

To accomplish this, i had to introduce a new default variable $cfg['pfxgen']['default_send_cmd']) to give the possibility to disable commands like conf tetc. (default True, to avoid breaking changes)

• Test / verify other ios
• contribute to readme.md
• ??

Let me know what you think.