MAINT: Use Python 3 compatible uuid hex property.
MAINT: Use Python 3 compatible uuid hex property.

Instead of `uuid`'s `get_hex()` use `hex` which is available in
both Python 2.7 and Python 3.

From: @chinux23, Chen Huang <5f6c5386f87c0f2a067e04f54aa18c618f19309d@apple.com>

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