Fix impersonation related bug in bigtable tests

[olchas]

This PR fixes bugs in two BigTable tests introduced in #10052 related to not including impersonation_chain in the list of arguments BigTableHook is called with.

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[olchas]

@potiuk I believe this might be the reason for broken master.

[potiuk]

@potiuk I believe this might be the reason for broken master.

Cool! Thanks! So this is one of those cases where two related changed crossed . I will cancel my revert then :)