Tests for bug when using `BayesianOptPro` in exclusively-`Categorical` with `FeatureEngineer`

[HunterMcGushion]

Conditions to summon bug (assume a blood offering has already been made):

1. Use BayesianOptPro
2. Use exclusively Categorical dimensions
3. At least one of the Categorical dimensions must be in FeatureEngineer

The above conditions will cause BayesianOptPro to break outright. However, problems still arise when omitting FeatureEngineer, while searching an exclusively multi-Categorical space. The effect of this bug is that saved experiment results are not properly marked as similar_experiments. Tests demonstrating the behavior of this second bug are added in 4b60f1a.

When the two xfail tests are marked as xpass, the bug is probably (hopefully) fixed

[codecov[bot]]

Codecov Report

Merging #152 into master will increase coverage by 0.13%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #152      +/-   ##
==========================================
+ Coverage   93.53%   93.67%   +0.13%     
==========================================
  Files          44       44              
  Lines        4393     4393              
==========================================
+ Hits         4109     4115       +6     
+ Misses        284      278       -6

Impacted Files	Coverage Δ
hyperparameter_hunter/optimization_core.py	92.9% <0%> (-0.34%)	:arrow_down:
hyperparameter_hunter/environment.py	98.72% <0%> (+0.42%)	:arrow_up:
hyperparameter_hunter/utils/optimization_utils.py	90.28% <0%> (+3.42%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update b4ff0cd...4b60f1a. Read the comment docs.

[coveralls]

Pull Request Test Coverage Report for Build 668

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.2%) to 93.763%

---

Files with Coverage Reduction	New Missed Lines	%
hyperparameter_hunter/optimization_core.py	2	93.92%
<!--	Total:	2		-->

Totals
Change from base Build 662:	0.2%
Covered Lines:	4119
Relevant Lines:	4393

---

💛 - Coveralls