Custom headers

[weinong]

---

This checklist is used to make sure that common guidelines for a pull request are followed.

General Guidelines

• Have you run azdev style <YOUR_EXT> locally? (pip install azdev required)
• Have you run python scripts/ci/test_index.py -q locally?

For new extensions:

• My extension description/summary conforms to the Extension Summary Guidelines.

[azuresdkci]

If this PR is for a new extension or change to an existing extension, use the following to try out the changes in this PR:

docker run -it microsoft/azure-cli:latest
export EXT=<NAME>
pip install --upgrade --target ~/.azure/cliextensions/$EXT "git+https://github.com/weinong/azure-cli-extensions.git@custom-headers#subdirectory=src/$EXT&egg=$EXT"

[yangl900]

will be super useful. thanks!

[fengzhou-msft]

please take a look at the travis log and fix the issue.

[weinong]

@fengzhou-msft fixed. thanks!

[weinong]

@haroldrandom @fengzhou-msft can we merge this soon?