Fix text output for single scalar value

Fixes the case where a `--query` arg produces a single
value.  For example, this now works as expected:

  $ aws ec2 create-key-pair --key-name testkey --query KeyMaterial --output text > ~/.ssh/foobar.pem
Merge branch 'single-scalar-text' into develop

* single-scalar-text:
  Fix text output for single scalar value