Remove vitrage-tempest-plugin from blacklist

This commit removes vitrage-tempest-plugin from the BLACKLIST since the
patch[0] was already merged.

NOTE: The patch on the comment[1] was duplicated of [0]. So it was
abandoned.

[0] https://review.opendev.org/#/c/638931/

Change-Id: I5539159bad10b3359981fab88b3be5e4e997fcb9
1 file changed