brocade: Use lazy logging interpolation

brocade: Use lazy logging interpolation

There are a small number of examples of "eager" interpolation in
neutron:
  logging.debug("foo %s" % arg)

These should be converted to perform the interpolation lazily within
the logging function, since if the severity is below the logging level
then the interpolation can be skipped entirely.

This change addresses all such examples found in brocade
l3_router_plugin via a pylint test.  Other occurrences are addressed
elsewhere.

Change-Id: Ia2d51e8ecbc7af81390577ec69c5ce18523b65f3
Partial-Bug: #1404788