Additional use of deferred imports to speed up pyutilib import

[jsiirola]

Fixes: #N/A

Summary/Motivation:

This makes additional use of deferred imports to avoid importing dependencies until the point where the dependencies are actually needed. This helps speed up the import of pyutilib, and by extension, dependent projects.

Changes proposed in this PR:

• defer the import of ConfigParser and yaml modules

Legal Acknowledgement

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1. I agree my contributions are submitted under the BSD license.
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[coveralls]

Coverage increased (+0.02%) to 61.08% when pulling 6e1e74f on jsiirola:deferred-imports into e6c1913 on PyUtilib:master.