Update Python container to correctly run "pip install cryptography"

[dcrankshaw]

If the user has a version of the cryptography library installed with pip, this change allows the model container to build it from source as the pip package requires. The cryptography library has C extensions, so it requires a compiler to build it.

In particular, this case is important to support because the clipper_admin pip package installs the cryptography as a dependency (by way of the fabric dependency).

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[nishadsingh1]

Checking this now. Also, is there a reason we don't preinstall clipper_admin? We could make a preinstalled pip package list whose elements we install after the conda ones.

[Corey-Zumar]

LGTM

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[dcrankshaw]

jenkins test this please

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[Corey-Zumar]

jenkins test this please

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