xenapi: changes the debug log formatting

This patch changes the log formatting to use multiple arguments instead
of interpolation.

Note:
It's a matter of performance :
When you do the interpolation in your code, this code will be executed
each time you call the logger (event if the logger or the log level is
not activated).
When you let the logger do the interpolation, it will do the interpolation
only if the logger and log level is activated.

Change-Id: I628000767f41bb0ab1839089a0ba98f6974c4635
Merge "xenapi: changes the debug log formatting"