Fix 'disk full' issue: Change objectstore exception handling

This patch changes __exit__ function of objectstore in order to log the
error information. It also changes the return to make python raise the
exception again, which will be caught by the functions that are using
the objectstore.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
Fix 'disk full' issue: Fix Templates db store/delete error handling

If disk is full and user tries to create a new template, Kimchi is going
to fail with "server unexpected error". The same problem happens if user
tries to delete a template. This patch modifies Templates code in order
to handle errors properly.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
Fix 'disk full' issue: Fix storage volume error handling

This patch fixes the error handling when storagevolume.py tries to
update the database with reference count information.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
Fix 'disk full' issue: Fix storagepool and asynctasks error handling

This patch fixes the error handling when storagepool.py and asynctask.py
try to update the objectstore (database) with task and scanning
information.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
Fix 'disk full' issue: Fix vms/screenshot db store/delete error handling

When creating, running or deleting a vm, it uses the database to store
vm and screenshot information. If the disk is full, Kimchi will raise
errors constantly and UI will be useless. This patch fixes this problem,
omitting from UI and logging in the backend. So, user is still able to
create, start and stop a vm.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>