AzureBlobFileSystem.mkdir seems to have no effect with exist_ok=True

[andersbogsnes]

What happened:
When creating a new directory using the AzureBlobFileSystem, mkdir has no effect if the exist_ok flag is True, even though the container does not exist.

What you expected to happen:
The container to be created, and if the code is run again, no exception will be raised

Minimal Complete Verifiable Example:

>>> from adlfs import AzureBlobFileSystem
>>> fs = AzureBlobFileSystem(account_name="myaccount", account_key="myaccountkey")
>>> fs.ls(".")
[]
>>> fs.mkdir("testcontainer", exist_ok=True)
>>> fs.ls(".")
[]
>>> fs.mkdir("testcontainer")
>>> fs.ls(".")
["testcontainer/"]

Anything else we need to know?:

Environment:

• adlfs version: 0.5.5
• Dask version: N/A
• Python version: 3.8
• Operating System: Ubuntu 20.04
• Install method (conda, pip, source): pip

[hayesgb]

Release 0.7.0 aligns adlfs mkdir() method to fsspec, per discussion here