Fix #901

[achimgaedke]

Description of Change

This PR specifies the encoding for any IMDS calls explicitly, this fixes #901.

[thehesiod]

is there a way to add a test for this?

[codecov]

Codecov Report

Merging #931 (fe4731d) into master (4694ba4) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #931   +/-   ##
=======================================
  Coverage   87.12%   87.12%           
=======================================
  Files          46       46           
  Lines        4969     4969           
=======================================
  Hits         4329     4329           
  Misses        640      640           

Flag	Coverage Δ
unittests	87.12% <100.00%> (ø)

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Impacted Files	Coverage Δ
aiobotocore/utils.py	71.09% <100.00%> (ø)
tests/botocore/test_utils.py	99.46% <100.00%> (ø)

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[thehesiod]

closing in favor of #934

[thehesiod]

closing in favor of #934