The only reason for importing nova.config now is where one of the
options defined in that file is needed. Rather than importing
nova.config using an import statement, use CONF.import_opt() so
that it is clear which option we actually require.
In future, we will move many options out of nova.config so many
of these import_opt() calls will either go away or cause a module
other than nova.config to be imported.
Change-Id: I0646efddecdf2530903afd50c1f4364cb1d5dce1
09cc03b31b