#2128 Add platform option for haul bundler

[z4o4z]

Issue:
#2128

What I did

Add platform option to storybook-cli;

How to test

storybook start -p 7007 --haul webpack.haul.storybook.js
storybook start -p 7007 --haul webpack.haul.storybook.js --platform ios
storybook start -p 7007 --haul webpack.haul.storybook.js --platform android

Is this testable with jest or storyshots?
No
Does this need a new example in the kitchen sink apps?
No
Does this need an update to the documentation?
Yes
If your answer is yes to any of these, please make sure to include it in your PR.

[codecov]

Codecov Report

Merging #2129 into master will increase coverage by 0.03%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #2129      +/-   ##
==========================================
+ Coverage    21.4%   21.43%   +0.03%     
==========================================
  Files         263      263              
  Lines        5812     5803       -9     
  Branches      694      702       +8     
==========================================
  Hits         1244     1244              
+ Misses       4039     4027      -12     
- Partials      529      532       +3

Impacted Files	Coverage Δ
app/react-native/src/bin/storybook-start.js	0% <0%> (ø)	⬆️
app/vue/src/server/config/babel.js	0% <0%> (-100%)	⬇️
app/vue/src/server/babel_config.js	0% <0%> (-77.42%)	⬇️
app/vue/src/server/utils.js	0% <0%> (-53.58%)	⬇️
...rc/modules/ui/components/left_panel/text_filter.js	30.98% <0%> (ø)	⬆️
lib/ui/src/modules/api/configs/init_api.js	40.47% <0%> (ø)	⬆️
addons/info/src/components/markdown/code.js	24.13% <0%> (ø)	⬆️
addons/knobs/src/components/PropForm.js	9.09% <0%> (ø)	⬆️
addons/knobs/src/react/WrapStory.js	19.54% <0%> (ø)	⬆️
app/react-native/src/bin/storybook-build.js	0% <0%> (ø)	⬆️
... and 18 more

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[danielduan]

looks reasonable to me. I migrated away from haul recently so I don't have another project to test this.