Wrap calls to fmt::format to catch formatting exceptions

fmt::format throws when a formatting error is encountered.
Unfortunately, we can't ensure complete coverage of all logging call
sites (e.g. error paths) and it is not desirable for such an exception
to be thrown in those cases.

The formatting error is returned as the formatted string so that it ends
up in the logs or exception messages more or less transparently.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I1cb33a5fe87221139eaf9de918b47e0397daa89c