Explicitly block Index ^ MultiIndex for Index.symmetric_difference

[itholic]

Related with #953 (comment) and #953 (comment)

[codecov-io]

Codecov Report

Merging #1059 into master will decrease coverage by 0.01%.
The diff coverage is 93.1%.

@@            Coverage Diff             @@
##           master    #1059      +/-   ##
==========================================
- Coverage   95.19%   95.18%   -0.02%     
==========================================
  Files          34       34              
  Lines        6810     6837      +27     
==========================================
+ Hits         6483     6508      +25     
- Misses        327      329       +2

Impacted Files	Coverage Δ
databricks/koalas/missing/indexes.py	100% <ø> (ø)	⬆️
databricks/koalas/indexes.py	96.05% <93.1%> (-0.43%)	⬇️

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[itholic]

the reason of codecov failure is we skip the doctest related with MiltiIndex since it would be shown different result depends on python version.
add test to tests/test_indexes.py for covering them

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