FIX: give useful error msg when bad URL passed to BlobClient.from_blob_url()

[pat-hearps]

Description

Problem: A user tries to use BlobClient.from_blob_url() with an incorrect URL that does not have a container name and blob path, e.g. BlobClient.from_blob_url("https://testaccount.blob.core.windows.net/containername/") - note the missing blobname after the containername
Current Behaviour: User gets obscure error message: Because the list path_blob only has length of 1, i.e. ["containername"].

>       container_name, blob_name = unquote(path_blob[-2]), unquote(path_blob[-1])
E       IndexError: list index out of range

Fixed Behaviour: raises more helpful error: ValueError("Invalid URL. Provide a blob_url with a valid blob and container name.")

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.
• Test 'test_from_blob_url_too_short_url()added totest_blob_client.py`

[ghost]

Thank you for your contribution pat-hearps! We will review the pull request and get back to you soon.

[ghost]

All CLA requirements met.

[jalauzon-msft]

Thanks for the contribution! Just one minor comment and then we should be able to get this merged.

[jalauzon-msft]

Thanks again @pat-hearps Patrick for your contribution! I've merged your change in and it will be part of the next release.