1. Use translation marker functions, their argument must just be a string
2. Any message with more than one variable should use named
interpolation instead of positional to allow translators
to move the variables around in the string to account for
differences in grammar and writing direction.
3. String interpolation should be delayed to be handled by the logging
code, rather than being done at the point of the logging call.
For more details, please refert to oslo.i18n guideline [1]
Note: this commit doesn't touch test code.
[1] http://docs.openstack.org/developer/oslo.i18n/guidelines.html
Change-Id: I5f013d65b20396bbe0e5a2cceaed2a33fad1af23
6b20fa8597