[Extension] fix loading wrong metadata for wheel type extension

[haroldrandom]

Description
With this #12782 merged, the ability to load metadata from a Python Package is enhanced, but the algorithm is to travel all folders under a specific extension home folder.

azure-cli/src/azure-cli-core/azure/cli/core/extension/__init__.py

Lines 146 to 151 in 69c9933

	for dist_info_dirname in info_dirs:
	try:
	ext_whl_metadata = pkginfo.Wheel(dist_info_dirname)
	metadata.update(vars(ext_whl_metadata))
	except ValueError:
	logger.warning('extension % contains invalid metadata for Python Package', self.name)

The problem is that if there are other folder named with .dist-info, it will load their metadata too, which will show a wrong extension version. Such as azure-iot and alias, as it has dependecies and CLI will place those dependecies inside the same folder for azure-iot.

$ ll ~/.azure/cliextensions/azure-iot           
total 568K
drwxrwxr-x 3 harold harold 4.0K Apr 28 11:25 attr
drwxrwxr-x 2 harold harold 4.0K Apr 28 11:25 attrs-19.3.0.dist-info
drwxrwxr-x 9 harold harold 4.0K Apr 28 11:25 azext_iot
drwxrwxr-x 2 harold harold 4.0K Apr 28 11:25 azure_iot-0.9.1.dist-info
-rw-rw-r-- 1 harold harold 289K Apr 28 11:25 azure_iot-0.9.1-py2.py3-none-any.whl
drwxrwxr-x 2 harold harold 4.0K Apr 28 11:25 bin
-rw-rw-r-- 1 harold harold  126 Apr 28 11:25 easy_install.py
drwxrwxr-x 6 harold harold 4.0K Apr 28 11:25 jsonschema
drwxrwxr-x 2 harold harold 4.0K Apr 28 11:25 jsonschema-3.0.2.dist-info
drwxrwxr-x 4 harold harold 4.0K Apr 28 11:25 paho
drwxrwxr-x 2 harold harold 4.0K Apr 28 11:25 paho_mqtt-1.5.0.dist-info
drwxrwxr-x 5 harold harold 4.0K Apr 28 11:25 pkg_resources
-rwxrwxr-x 1 harold harold 166K Apr 28 11:25 pvectorc.cpython-36m-x86_64-linux-gnu.so
drwxrwxr-x 2 harold harold 4.0K Apr 28 11:25 __pycache__
drwxrwxr-x 3 harold harold 4.0K Apr 28 11:25 pyrsistent
drwxrwxr-x 2 harold harold 4.0K Apr 28 11:25 pyrsistent-0.16.0.dist-info
-rw-rw-r-- 1 harold harold   23 Apr 28 11:25 _pyrsistent_version.py
drwxrwxr-x 6 harold harold 4.0K Apr 28 11:25 setuptools
drwxrwxr-x 2 harold harold 4.0K Apr 28 11:25 setuptools-46.1.3.dist-info
drwxrwxr-x 2 harold harold 4.0K Apr 28 11:25 six-1.14.0.dist-info
-rw-rw-r-- 1 harold harold  34K Apr 28 11:25 six.py

That's why causing this bug.

Testing Guide
Before fix, try install azure-iot extension, then az extension list -o table it will show a wrong version instead of its current version 0.9.1
After fix, it will show 0.9.1

History Notes

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[yonzhan]

add to S170

[fengzhou-msft]

verified locally with azure-iot.

[haroldrandom]

Fix Azure/azure-iot-cli-extension#173