ansible: 2_ovirt_logger.py: Improve logging
ansible: 2_ovirt_logger.py: Improve logging

- Log more data in dump_obj, up to 4096 chars instead of 300. Both are
arbitrary, but 300 is too short for some useful messages.
- Clarify that we shortened the data using a new function
_shorten_string.
- On failure, instead of dump_obj use _pretty_logging

Change-Id: I217b7e5eb46d4a0793f78badff8914dfeb83a6ee
Signed-off-by: Yedidyah Bar David <e7f2f616ce8817ad893bbeaad3e942e94c69d323@redhat.com>

oVirt/ovirt-hosted-engine-setup,oVirt/ovirt-hosted-engine-setup