Error handling in GRIP-api

[VijayrajS]

Currently the API does not return specific error codes (it is either a 200 or a 500 internal server error).

The following cases should be handled for the API endpoints:

• When the format of the event id is wrong (400) (Reference for format of event IDs are in grip-core (grip/events/pfxevent.py, grip/events/details_<event_type>.py)
• When the format is fine, but the event does not exist (404)
• '/pfx_event/id//': Note: Check if event ID is available and if the prefix is available and valid too (all permutations) - prefix validity (400) and whether it does not belong to this event (404) (You can use ip address library to check validity of prefix)
• When the elasticsearch instance is down (should be 500 or 503 - check this once, service unavailable)
• Have a common function to check for event ID validity.

[VijayrajS]

Observation: if we try hitting the pfx_event endpoint with missing ID/prefix, it sends a 404 back because it is not a URL recognized by the Flask App