xCluster: Script Analyzer warnings that need to be fixed

[johlju]

The following PSScriptAnalyzer errors need to be fixed:
MSFT_xCluster.psm1 (Line 25): $null should be on the left side of equality comparisons.
MSFT_xCluster.psm1 (Line 25): $null should be on the left side of equality comparisons.
MSFT_xCluster.psm1 (Line 81): $null should be on the left side of equality comparisons.
MSFT_xCluster.psm1 (Line 81): $null should be on the left side of equality comparisons.
MSFT_xCluster.psm1 (Line 186): $null should be on the left side of equality comparisons.
MSFT_xCluster.psm1 (Line 186): $null should be on the left side of equality comparisons.
MSFT_xCluster.psm1 (Line 24): File 'MSFT_xCluster.psm1' uses WMI cmdlet. For PowerShell 3.0 and above, use CIM cmdlet which perform the same tasks as the WMI cmdlets. The CIM cmdlets comply with WS-Management (WSMan) standards and with the Common Information Model (CIM) standard, which enables the cmdlets to use the same techniques to manage Windows computers and those running other operating systems.
MSFT_xCluster.psm1 (Line 80): File 'MSFT_xCluster.psm1' uses WMI cmdlet. For PowerShell 3.0 and above, use CIM cmdlet which perform the same tasks as the WMI cmdlets. The CIM cmdlets comply with WS-Management (WSMan) standards and with the Common Information Model (CIM) standard, which enables the cmdlets to use the same techniques to manage Windows computers and those running other operating systems.
MSFT_xCluster.psm1 (Line 185): File 'MSFT_xCluster.psm1' uses WMI cmdlet. For PowerShell 3.0 and above, use CIM cmdlet which perform the same tasks as the WMI cmdlets. The CIM cmdlets comply with WS-Management (WSMan) standards and with the Common Information Model (CIM) standard, which enables the cmdlets to use the same techniques to manage Windows computers and those running other operating systems.