SqlServerDsc: Fix minor review comments

[johlju]

Reviewed 10 of 10 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @johlju)

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azure-pipelines.yml line 194 at r1 (raw file):

              Remove-Module -Name CommonTestHelper
            name: removeSqlServerModule
            displayName: 'Remove SqlServer module'

Can be fixed in another PR.

Suggestion:

'Clean CI worker'

---

azure-pipelines.yml line 296 at r1 (raw file):

              Remove-Module -Name CommonTestHelper
            name: removeSqlServerModule
            displayName: 'Remove SqlServer module'

Can be fixed in another PR.

Suggestion:

'Clean CI worker'

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source/Public/Import-SqlDscPreferredModule.ps1 line 113 at r1 (raw file):

            $modulePathMachine = [System.String] [System.Environment]::GetEnvironmentVariable('PSModulePath', 'Machine')

            $modulePath = $modulePathSession + ';'  + $modulePathUser + ';' + $modulePathMachine

Can be fixed in another PR.

Suggestion:

$modulePath = $modulePathSession, $modulePathUser, $modulePathMachine -join ';'

Originally posted by @johlju in #1877 (review)