Port to graduated library oslo.i18n

log_handler is not used any more by Ceilometer project, but still
listed on openstack-common.conf, this patch fixes it.

Note: oslo-incubator.timeutils is not used by oslo-incubator modules
any more after we do code sync, this patch removes it too.

gettextutils has graduated from oslo-incubator, we should port our
project to use oslo.i18n. To use oslo.i18n conveniently, this patch
introduces a helper module ceilometer.i18n, which is stolen from Nova.

Note: gettextutils.install is deprecated, see:
http://docs.openstack.org/developer/oslo.i18n/usage.html#creating-an-integration-module
Note: _ is removed from builtins in tox.ini since we're not using
install any more.

Change-Id: I829f9faf97c825422b395bf9c01ae5c17c86d9fb
Closes-Bug: #1389546