Just tested this out on one of their x86 instances and it works, so the issue is plesk isn't compatible with their ARMv7 instances.
Thanks going to vote for this.:)
This is what I get:
https://autoinstall.plesk.com/Parallels_Installer/parallels_installer_Ubuntu_14.04_armv7l
Resolving autoinstall.plesk.com (autoinstall.plesk.com)... 185.59.222.22
Connecting to autoinstall.plesk.com (autoinstall.plesk.com)|185.59.222.22|:80... connected.
HTTP request sent...