Device wants desperately to install a package (com.google.system.s) on its own
From experience, flashing in any conventionally accepted way instantaneously bricks this Mpie M8. It takes a lot of efforts to unbrick it, too. So work with what you have, root it first so that the malware can be managed. When the auto-installation-without-permission starts, pull down notification and click on app info to see which system process is being hijacked and disable it immediately. As an example, mine shows Launcher and Android Service are involved. Have used a different launcher instead just to be on the safe side. Android Service, hiding in /system/priv-app as android_service_800000_0923_outsea.apk, appears the true culprit. Once deleted, the phone runs flawlessly. Of course your phone may have different malware in it depending on which malicious websites that you have visited. Good luck.