Set raise_error to default to True for AutoML classes

[angela97lin]

Closes #635

[codecov]

Codecov Report

Merging #638 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #638   +/-   ##
=======================================
  Coverage   98.97%   98.97%           
=======================================
  Files         136      136           
  Lines        4685     4692    +7     
=======================================
+ Hits         4637     4644    +7     
  Misses         48       48           

Impacted Files	Coverage Δ
evalml/automl/auto_base.py	96.36% <100.00%> (ø)
...ts/automl_tests/test_auto_classification_search.py	100.00% <100.00%> (ø)
.../tests/automl_tests/test_auto_regression_search.py	100.00% <100.00%> (ø)
evalml/tests/automl_tests/test_autobase.py	100.00% <100.00%> (ø)
...alml/tests/objective_tests/test_fraud_detection.py	100.00% <100.00%> (ø)
evalml/tests/objective_tests/test_lead_scoring.py	100.00% <100.00%> (ø)

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[dsherry]

Left a minor comment and a question, LGTM!