Address warnings from dependencies

[felker]

Trying to prevent the noise in stdout from the following packages:

• matplotlib: from calling matplotlib.use() after certain import statements
• numpy: from versions >= 1.6.3 from np.load() changes in response to https://nvd.nist.gov/vuln/detail/CVE-2019-6446
• yaml: also a change in default loading behavior for security reasons

[buildbot-princeton]

Can one of the admins verify this patch?

[ASvyatkovskiy]

Add to whitelist