Fix indentation errors in tests

Fix indentation errors in tests

They are some missing/extra indentations in tests source code. This
results in variables used out their scope (which remains unnoticed as
long as `with` contexts do not fail), and prevent refactoring scripts
(such as the one for getting rid of `contextlib.nested` [1]) from
performing well.

This simple patch fixes these indentation errors.

[1]: See change I8d1de09ff38ed0af9fb56f423a2c43476408e0fb

Change-Id: Icef34c7755e0d96c4c5ee85982de86d0ccc196c7
Related-Blueprint: neutron-python3