Fix bug when testing multiindex dtypes in assert_frame_equal and assert_series_equal
Merge pull request #8042 from artemyk/fix-assert_frame_equal-multiindex-dtypes

Fix testing multiindex dtypes in assert_frame_equal and assert_series_equal
TST: skip test_kds_colors if too old scipy installed
BUG: stack with datetimes

Just take from index itself, not levels.