Make local mode querystring processing consistent with APIGateway

[stealthycoin]

closes: #964

[codecov-io]

Codecov Report

Merging #965 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #965   +/-   ##
=======================================
  Coverage   95.52%   95.52%           
=======================================
  Files          27       27           
  Lines        4449     4449           
  Branches      558      558           
=======================================
  Hits         4250     4250           
  Misses        128      128           
  Partials       71       71

Impacted Files	Coverage Δ
chalice/local.py	99.36% <100%> (ø)	⬆️

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[kyleknap]

🚢

[stealthycoin]

Just to show it matches API Gateway:

from chalice import Chalice

app = Chalice(app_name='test-query')


@app.route('/')
def index():
    return 'args: %s' % app.current_request.query_params

$ curl "localhost:8000/?a=1&a=2"
args: {'a': '2'}

$ curl $(chalice url)"?a=1&a=2"
args: {'a': '2'}