Add 2 tests to the Floating IP test case

Associate a Floating IP to a port and then delete it
Associate a Floating IP to a port and then to a port on another
router

Change-Id: I37bb7c348db8767571f95db35df0545d366b5d10
Implements: blueprint add-test-neutron-tempest-floating-ip
Increase exception log details

Add informative message to log, as the exception is logged by default

Replaces:
except Exception as exc:
    LOG.exception(exc)

With:
except Exception:
    LOG.exception("[Description of the failed operation]")

Closes-bug: #1262547

Change-Id: I97cd13e4b32df9a3f9b2e7e1f8946a6a4e0aed3f
Merge "Add 2 tests to the Floating IP test case"
Merge "Increase exception log details"