Make it possible to respond with different version arguments based on `is_machine` parameter on update check

[shashkin]

When talking about Omaha+Chromium, there is already workaround for Chromium inside Omaha client code, which handles this scenario on client side.

In general, however, it would be great if the server can manage this by itself so we don't depend on any particular application like Chromium.

[shashkin]

Possible design change: split "Arguments" field of Omaha Version into three fields:

• "Common arguments" - arguments which are the same for per-user and per-machine installations
• "Per-user arguments" - arguments only applicable for per-user installation
• "Per-machine arguments" - arguments only applicable for per-machine installation

Depending on is_machine value, the server will respond arguments as concatenation of "common" and "per-user/per-machine" arguments