Fix msiexec hang on Windows — add /qn /norestart to install.ps1

[musa-asad]

Summary

Fixes indefinite msiexec hang during CloudWatch Agent installation on Windows when another MSI is already in progress (error 1618).

Without /qn, msiexec shows a UI dialog on error. In Session 0 (non-interactive), this dialog is invisible and blocks indefinitely until the calling process times out.

Changes

packaging/windows/install.ps1 line 17:

• Added /qn (quiet, no UI) — ensures msiexec runs in silent mode so errors return exit codes instead of showing dialogs
• Added /norestart — prevents unexpected reboots on hosts managed via automation
• Added -PassThru and exit code check — throws on non-zero exit so failures are reported instead of silently proceeding to cond-restart
• Exit code 3010 (success, reboot required) is treated as success since /norestart suppresses the reboot

uninstall.ps1 is NOT affected (uses WMI, not msiexec).

Before (hangs on error, no exit code check):

Start-Process msiexec.exe -Wait -ArgumentList '/i amazon-cloudwatch-agent.msi'

After (returns immediately, fails explicitly):

$proc = Start-Process msiexec.exe -Wait -PassThru -ArgumentList '/i amazon-cloudwatch-agent.msi /qn /norestart'
if ($proc.ExitCode -ne 0 -and $proc.ExitCode -ne 3010) {
    throw "msiexec failed with exit code $($proc.ExitCode)"
}

Testing

Reproduced on Windows Server 2025. Process evidence confirmed: msiexec PID stuck in Session 0 with invisible Windows Installer dialog, ThreadWaitReason=UserRequest. MSI mutex NOT held — confirms dialog-wait, not mutex-wait. With /qn, msiexec returns error 1618 immediately instead of hanging. Exit code check ensures real errors propagate while 3010 (reboot-needed) is accepted.