provide an option to specify that the cli is being used in a non-interactive session

[snowch]

I frequently use the bx cli in scripts that don't have a human to interact with them. Occasionally, the sdk prompts for input which requires messy code to handle this interaction programatically.

An example prompt:

! bx login --apikey @'/mydir/myapikey.json'

Results in:

API endpoint: https://api.ng.bluemix.net
Authenticating...
OK
...
A new version of Bluemix CLI is available. Do you want to update? (yes/no) [yes]>

It would be great if I could tell the cli that I don't want these prompts. Here is one example from debian telling the cli that it shouldn't prompt for user input:

DEBIAN_FRONTEND=noninteractive apt-get ...

I think in terms of updating the bx cli, the default response should be 'no' in noninteractive mode.

[snowch]

It looks as though I can avoid the update prompt by running:

bx config --check-version false