bin/master.py has a logging call with invalid formatting.

This came up in #755 (closed) There is a call in bin/master.py

                log.info("""\
Runner {0} reached maximum restart limit of {1:d}, not restarting.""",
                         rname, max_restarts)

which is invalid because the logging module uses % interpolation, not str.format(). This needs to be changed to

                log.info("""\
Runner {0} reached maximum restart limit of {1:d}, not restarting.""".format(
                         rname, max_restarts))