Fix test timing out due to module scan

Author: ericsciple

Tasks/Common/VstsAzureHelpers_/Tests/Import-AzureModule.ThrowsWhenNotFound.ps1

@@ -4,17 +4,16 @@ param()
 # Arrange.
 . $PSScriptRoot\..\..\..\..\Tests\lib\Initialize-Test.ps1
 $module = Microsoft.PowerShell.Core\Import-Module $PSScriptRoot\.. -PassThru
+Register-Mock Import-FromModulePath
+Register-Mock Import-FromSdkPath
+Register-Mock Discover-AvailableAzureModules
 $variableSets = @(
     @{ PreferredModule = 'Azure', 'AzureRM' }
     @{ PreferredModule = 'Azure' }
     @{ PreferredModule = 'AzureRM' }
 )
 foreach ($variableSet in $variableSets) {
     Write-Verbose ('-' * 80)
-    Unregister-Mock Import-FromModulePath
-    Unregister-Mock Import-FromSdkPath
-    Register-Mock Import-FromModulePath
-    Register-Mock Import-FromSdkPath
 
     # Act/Assert.
     Assert-Throws { & $module Import-AzureModule -PreferredModule $variableSet.PreferredModule -azurePsVersion "4.1.0" } -MessagePattern "AZ_ModuleNotFound 4.1.0"