Misc: Cib model: Use Util.numeric? for selecting instances

Signed-off-by: Tim Serong <tserong@suse.com>

Commit 489e655 was using to_i to check if an instance ID was
numeric, or was :default.  On ruby 1.8, to_i is valid for
symbols, so you'd sometimes get crazy instance IDs (e.g.: 7186).
This is fixed by using Util.numeric? instead.
GUI: Status: Show fail counts for clone instances (bnc#808047)

Signed-off-by: Tim Serong <tserong@suse.com>