Replace variables in host.json using Octopus.ps1

    # replace Octopus variables in host.json
    $octoVariableRegEx = [regex]"#\{([A-Za-z0-9_]+)\}"
    $matchEvaluator = { 
        $varName = $args[0].Groups[1]
        $octoValue = $global:OctopusParameters[$varName]
        if ($null -ne $octoValue) { $octoValue } else { "$varName NOT DEFINED!" }
    }
    $hostJsonFiles = Get-ChildItem -Recurse $functionPackage -Filter 'host.json'
    if ($hostJsonFiles.Count -gt 0) {
        $hostJsonFile = $hostJsonFiles[0].FullName
        $hostJsonOrig = Get-Content $hostJsonFile -Raw
        $hostJsonReplaced = $octoVariableRegEx.Replace($hostJsonOrig, $matchEvaluator)
        $hostJsonReplaced | Set-Content $hostJsonFile
    }