Update revocation demo

[nrempel]

Update revocation demo to support old tails server environment variable for backwards compatibility and documentation alignment

[codecov-commenter]

Codecov Report

Merging #644 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #644   +/-   ##
=======================================
  Coverage   98.70%   98.70%           
=======================================
  Files         250      250           
  Lines       13385    13385           
=======================================
  Hits        13211    13211           
  Misses        174      174           

[lgtm-com]

This pull request introduces 2 alerts when merging c286654 into 31f1c87 - view on LGTM.com

new alerts:

• 2 for Unused import

[ianco]

Is --revocation supposed to work without an external tail server? When I run ./run_demo faber --revocation without any other parameters/options I get an error:

Traceback (most recent call last):
  File "/home/indy/demo/runners/support/agent.py", line 452, in admin_request
    resp.raise_for_status()
  File "/home/indy/.pyenv/versions/3.6.9/lib/python3.6/site-packages/aiohttp/client_reqrep.py", line 946, in raise_for_status
    headers=self.headers)
aiohttp.client_exceptions.ClientResponseError: 400, message='tails_server_base_url not configured', url=URL('http://192.168.65.3:8021/credential-definitions')

[ianco]

• see pr on the ngrok-wait.sh script
• when starting faber with --revocation make sure tails url is supplied

[lgtm-com]

This pull request introduces 2 alerts when merging 96a9c9b into 31f1c87 - view on LGTM.com

new alerts:

• 2 for Unused import

[andrewwhitehead]

Up to @ianco to approve as it's waiting on his changes requested