test: azure: test_open is failing on azure-storage-blob > 1.5.0

[efiop]

See https://travis-ci.com/iterative/dvc/jobs/224085273 .

It turnes out that azure python sdk modified the way they are calculating sas token in Azure/azure-storage-python@a79f8d8#diff-6ded9db46a5b567ba052e1e9d3c16acd (by adding KEY_VERSION and friends) and so now stringToSign computed in azurite https://github.com/Azure/Azurite/blob/v3.1.2-preview/src/blob/authentication/IBlobSASSignatureValues.ts#L168 doesn't match the one in https://github.com/Azure/azure-storage-python/blob/master/azure-storage-blob/azure/storage/blob/sharedaccesssignature.py#L226 . I will report this to azurite guys, but for now we could simply use 1.5.0 for our tests. We can't move to 1.5.0 permanently, because things like our conda package need 2.1.0.

For the record, this issue wasn't caught while #2371 was tested on CI because we still don't run those tests on regular PRs (we run them only on master) and the author used an old azure python sdk while testing it on his machine.

EDIT: Azure/Azurite#250

[efiop]

Fixed by #2785