a-a-ureport: handle os errors gracefully rhbz#998428 rhbz#998197

Now it won't crash when its working directory is deleted
or when it's not able to spawn a process or it tries to spawn
missing binary. It spits proper error message instead of exception.

Signed-off-by: Richard Marko <rmarko@redhat.com>
Merge pull request #705 from abrt/rhbz998428

a-a-ureport: handle os errors gracefully rhbz#998428 rhbz#998197