Translator functions cleanup part 4

This part fixes ironic/api, ironic/cmd, ironic/tests folders.

Some modules use _ function for log translation, even when the
translated string is passed to e.g. LOG.warn function. This patch
fixes it, using translator functions appropriate for corresponding
log levels. Translator functions, imported from
ironic.openstack.common.gettextutils are now imported from
ironic.common.i18n. Translator functions are imported the same way
across all modules. All places that are changed conform to
http://docs.openstack.org/developer/oslo.i18n/guidelines.html

Partial-bug: #1364813

Change-Id: I92e5f0d50c3b507080fb95e81274a241558ce526
Merge "Translator functions cleanup part 4"