Include handler's dependencies to the archived env yml

[yubozhao]

Include handler's dependencies as well, when we are archiving bento service

[codecov-io]

Codecov Report

Merging #218 into master will decrease coverage by 0.11%.
The diff coverage is 92.3%.

@@            Coverage Diff             @@
##           master     #218      +/-   ##
==========================================
- Coverage   52.45%   52.34%   -0.12%     
==========================================
  Files          53       55       +2     
  Lines        2949     3051     +102     
==========================================
+ Hits         1547     1597      +50     
- Misses       1402     1454      +52

Impacted Files	Coverage Δ
bentoml/handlers/base_handlers.py	72.97% <100%> (+1.54%)	⬆️
bentoml/handlers/image_handler.py	59.37% <100%> (+0.86%)	⬆️
bentoml/handlers/fastai_image_handler.py	35.15% <100%> (+1.29%)	⬆️
bentoml/service.py	87.15% <100%> (+0.14%)	⬆️
bentoml/service_env.py	64.48% <75%> (+0.4%)	⬆️
bentoml/deployment/sagemaker/__init__.py	20.86% <0%> (-1.13%)	⬇️
bentoml/cli/click_utils.py	87.17% <0%> (-1.06%)	⬇️
bentoml/utils/log.py	100% <0%> (ø)	⬆️
bentoml/cli/deployment.py	54.54% <0%> (ø)
bentoml/cli/config.py	26.76% <0%> (ø)
... and 2 more

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