Fail Gulp task if PowerShell scripts fail

[uli-weltersbach]

When a Gulp-task calls a PowerShell script, ensure a non-zero exit code causes the Gulp-script to fail.

E.g. Install-Packages.ps1:

foreach ($package in $packages.packages) {
    Install-NugetPackage -package $package -webRootPath $webRootPath -dataRootPath $dataRootPath -username $username -password $password
}

Gulp will return an exit code of zero even when one of the Install-NugetPackage-calls fails, the user doesn't have administrative privileges to run the script etc.

[melker]

If the task had returned a proper error code it would have saved me 2 full days of work looking for all kinds of other errors. :-(
Please fix @Hafeok so others don't have to do the same.