Write UT and improve coverage for alibaba cloud

[PravinRanjan10]

Issue/Feature Description:

Improve coverage by wriring UT for alibaba cloud file ==>[pkg/s3/datastore/alibaba]

Why this issue to fixed / feature is needed(give scenarios or use cases):

How to reproduce, in case of a bug:

Other Notes / Environment Information: (Please give the env information, log link or any useful information for this issue)