Removes log generation parameters from EXTRA_OPTS

Reasons:
- No need of using these parameters.
- Logging could be managed on its own by nova.
- Would help to reduce logfiles generation,
  hence making the maintenance easier.
- All other components are already doing this way.

Changes:
- Removed logdir from EXTRA_OPTS.
- Removed logfile_mode from EXTRA_OPTS.

If needed by user, one can modify the nova.conf to
generate logfiles at their desired location.

Change-Id: I301b8a2fa1522965442efa72e21085389ee662f8
Closes-Bug: #1260648
Merge "Removes log generation parameters from EXTRA_OPTS"