subiquity does not include a SystemIdentifier in its crash reports

When whoopsie sends in a crash report it adds a SystemIdentifier to the crash which uniquely identifies the system so that other crashes from the same system can be found. While this might not be immediately useful for subiquity crashes I think it'd be best (for consistency and just in case) if the SystemIdentifier was included.

In the whoopsie source code you can find this in identifier.c.