Add error handling for XGBoost

[ndodda-amazon]

Description of changes:

Add error handling for XGBoost. Defined a new has_default_hook_configuration for XGBoost since the default XGBoost collections do not match the general default collections.

Also defined a new function set_mode in KerasHook that gets wrapped with error handler and removed the error handling from the base hook's set_mode function. This is because set_mode is only called in the default smdebug configuration for TF, but not the other frameworks.

Style and formatting:

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Issue number, if available

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[codecov-commenter]

Codecov Report

Merging #496 (3b4d029) into master (8dccd06) will decrease coverage by 0.03%. The diff coverage is 41.66%.

@@            Coverage Diff             @@
##           master     #496      +/-   ##
==========================================
- Coverage   72.59%   72.56%   -0.04%     
==========================================
  Files         115      115              
  Lines       10382    10383       +1     
==========================================
- Hits         7537     7534       -3     
- Misses       2845     2849       +4     

Impacted Files	Coverage Δ
smdebug/xgboost/hook.py	0.00% <0.00%> (ø)
smdebug/xgboost/singleton_utils.py	0.00% <0.00%> (ø)
smdebug/core/hook.py	90.28% <100.00%> (+0.33%)	:arrow_up:
smdebug/tensorflow/base_hook.py	73.52% <100.00%> (-0.29%)	:arrow_down:

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