DI-930 fix #207 strip whitespace from inputs

[jethror1]

• adds new function CheckInputs.strip_string_inputs to ensure all string inputs have no leading / trailing whitespace
  • fixes #207
• add unit test for new function

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This change is 

[pep8speaks]

Hello @jethror1! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file resources/home/dnanexus/dias_batch/dias_batch.py:

Line 270:80: E501 line too long (84 > 79 characters)