Deploy fails with unclear error message when `MIST_HOST` param is not specified

[shilgam]

Weird error message before paramMIST_HOST was specified:

function git:(km/poc) ✗ pip install mist-cli==1.0.3
... 
Successfully installed mist-cli-1.0.3
➜  function git:(km/poc) ✗
➜  function git:(km/poc) ✗ mist-cli apply -f deploy --validate false
Process 3 file entries
updating Artifact ishakirov_visit_metrics_0.0.1.jar
Error: HTTPConnectionPool(host='localhost', port=2004): Max retries exceeded with url: /v2/api/artifacts?force=True (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x10c4c94a8>: Failed to establish a new connection: [Errno 61] Connection refused',))
updating Context ishakirov_visit_metrics_poc
Error: HTTPConnectionPool(host='localhost', port=2004): Max retries exceeded with url: /v2/api/contexts (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x10c4c9cf8>: Failed to establish a new connection: [Errno 61] Connection refused',))
updating Function ishakirov_visit_metrics_visitsAfterExposure
Error: HTTPConnectionPool(host='localhost', port=2004): Max retries exceeded with url: /v2/api/functions?force=True (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x10c4d2438>: Failed to establish a new connection: [Errno 61] Connection refused',))
➜  function git:(km/poc) ✗
➜  function git:(km/poc) ✗

Deploy was finished successfully only after MIST_HOST param was specified:

➜  function git:(km/poc) ✗ export MIST_HOST=dev-pca-mist.singularity.k.9dev.io

[blvp]

We can disable default values for --host and --port parameters, but it is not very handy for development. Even if we disable default values, we can achieve this kind of error when simply wrong url is passed.