Fixed message truncation bug

[allfro]

The length of the utf-8 encoded body may be different than the unicode length of the string. This causes message truncation on the response. This patch fixes the issue.

Description of changes:
Moved the code that converts the body to bytes up a few lines to reside before the code that sends the Content-Length header

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #910 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master     #910   +/-   ##
=======================================
  Coverage   95.48%   95.48%           
=======================================
  Files          27       27           
  Lines        4449     4449           
  Branches      558      558           
=======================================
  Hits         4248     4248           
  Misses        129      129           
  Partials       72       72

Impacted Files	Coverage Δ
chalice/local.py	98.73% <0%> (ø)	⬆️

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[stealthycoin]

Looks good to me. I am going to add a test for this.