Add basic lazy gettext implementation

This is the first part of an implementation towards
a deferred localization functionality in OpenStack.
This change adds a Message class for encapsulating a
translatable message and its relevant data, as well
as an example LogHandler of how such a class can be
used in the logging context.

bp delayed-message-translation

Change-Id: I8485a346d32925327ea9185e0da3822e4e19c2f5
Add common code for fileutils.

This code is present in nova, cinder and also needed by ironic package.
* delete_if_exists
* remove_path_on_error

Also added some tests.

openstack/common/fileutils.py => nova.common.utils <=> cinder.common.utils

Change-Id: Id5001db161bb8e7dfb20d1b2cc2033e886cda32f
Implements: blueprint image-tools
Merge "Add common code for fileutils."
Added common code into fileutils and strutils.

This methods are present in nova, cinder and also needed by ironic package.

openstack.common.strutils => nova.utils <=> cinder.utils
    to_bytes(text, default=0)

openstack.common.fileutils => nova.utils <=> cinder.utils <=> nova/virt/libvirt/utils.py
    file_open(*args, **kwargs)

Change-Id: Ia65499b77eb551c0ffb6d48767b899435469bfb6
Implements: blueprint image-tools
Merge "Add basic lazy gettext implementation"
Add fileutils maintainer

Change-Id: I1f909a84589ef173ac4e858e4c27a8a536d991ba