Installer does not report out-of-disk-space error if disk space runs out

[drojf]

If disk space runs out during the download phase, the installer will report a generic error about the download stage failing, rather than explicitly telling you that disk space ran out (this might also happen during extraction with 7zip). This is mainly because we don't properly parse the output of aria2c to determine the error (even just copying the first line of the error message from aria2c may be better).

The installer should parse the aria2c output to see if disk space ran out, then immediately exit and report out-of-disk space.

TODO:

1. Report less generic error if disk space runs out
2. Stop download/extract immediately if disk space runs out (currently will retry 3 times!)
3. Log disk space on both drives (the target drive and the 'current' drive used for temp files) to installer log (currently neither is logged!)