qdev: improve property error reporting.

qdev: improve property error reporting.

Add a error message in case we fail to parse a qdev property.

Also make qemu not abort() in case setting a global property can't be
set.  This used to be a clear programming error.  The introduction of
the -global switch changed that though, so better exit instead (after
printing the new error message).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>