Fixing typo "existant". Must be "existent"

Negative tests that use the word "existant" are being corrected to "existent".
The current framework has random usage of the word 'existant' instead of
'existent'.

Change-Id: I4219c372befbd8235757f124d1414317d9b01f72
Merge "Fixing typo "existant". Must be "existent""