Fix some testifylint warnings.

[atombrella]

Description

Fixed some testifylint warnings. Please go over your linting report. There are quite a lot of findings.

• a.Nil(err) -> a.NoError(err)
• a.True(string.Contains(...)) -> a.Contains(...) this was not a consistent change, though
• a.NotEqual(0, len(-)) -> a.NotEmpty(-)
• Fixed a single case of an if-else that can be a switch
• else { if should be else if
• VSCode sorts imports. This is also pretty peculiar why this odd sorting has survived for so long in a project. I already created Format files according to goimports #3254 for the same thing.

I use this software as an Azure customer.

Type of Change

• Bug fix
• New feature
• Documentation update required
• Code quality improvement
• Other (describe):

How Has This Been Tested?

Compiling should be fine.

Thank you for your contribution to AzCopy!