Support CondaKernelSpecManager.env_filter regex

[parente]

In some deployments, there may be conda environments present that
should not appear in the list (e.g., environments that may have
jupyter, python, R but not kernels)

[coveralls]

Coverage increased (+0.1%) to 74.17% when pulling 3c47982 on parente:env-filter into fa870f1 on Anaconda-Platform:master.

[coveralls]

Coverage increased (+0.1%) to 74.17% when pulling 3c47982 on parente:env-filter into fa870f1 on Anaconda-Platform:master.

[ericdill]

@damianavila @bollwyvl any chance of reviewing this?

[damianavila]

Sorry for the delay @ericdill and @parente... this is useful.
I like it, let's wait (for a little bit) for @bollwyvl 's look as well, otherwise I will merge it in a few days.

[bollwyvl]

Yeah, looks good. Let's merge and move forward. I'll make some issues for some miscellany...

[parente]

Cool. Thanks!