SaltStack Grains Python Function

Adding a python function to salt grains, that can provide a value from each minion.
- The requirement was to get the external ip from a minion
Write the python function that returns the grains value and place it in your salt stack dir structure in ./salt/_grains/grains-external-ip.py
- The actual python file name does not matter.
```
   1 #!/usr/bin/python
   2 '''
   3 Grain should return a dict, name of file does not matter
   4 '''
   5 import requests
   6 import socket
   7 import logging
   8 log = logging.getLogger(__name__)
   9 
  10 def external_ip():
  11     '''
  12     Return the external IP address reported by ipecho.net
  13     '''
  14     hostname = socket.gethostname().upper()
  15     log.debug("grain example hostname: " + hostname)
  16     # initialize a grains dictionary
  17     grains = {}
  18 
  19     try:
  20         r = requests.get('http://ipecho.net/plain')
  21         ip = r.content
  22     except:
  23         ip = ''
  24 
  25     grains['external_ip'] = ip
  26     grains['anothergrain'] = 'somevalue'
  27     return grains
  28 
  29 
  30 if __name__ == "__main__":
  31     print( external_ip() )
```
Once saved on a salt minion with sudo salt-call or from salt master with sudo salt "<Minion>" refresh grains and retrieve value.
- ```
sudo salt "minion1" saltutil.sync_grains
sudo salt "minion1" grains.get external_ip
minion1:
    71.43.13.6
```
once the grains function works, you might want to add it to the salt mine, to make it available to other nodes/minions.
- Add to file pilla/common/mine.sls
  - ```
  #external_ip calculated by salt/_grains/grains-get-externalip.py
    external_ip:
      mine_function: external_ip
```