api: provide api definition over api

api: provide api definition over api

This patch allows a client to bootstrap itself by downloading the
JSON API definitions over the API itself.

This patch enables it for Python (probably need a dynamic language).
Call VPPApiClient with the new bootstrapapi=True parameter.

Example (Python):

from vpp_papi import VPPApiClient
vpp = VPPApiClient(bootstrapapi=True)
rv = vpp.connect("foobar")
assert rv == 0
print(f'SHOW VERSION: {vpp.api.show_version()}')
vpp.disconnect()

Type: feature
Change-Id: Id903fdccc82b2e22aa1994331d2c150253f2ccae
Signed-off-by: Ole Troan <otroan@employees.org>