If for some reason there is an existing log file, that is larger then
max length of log file, we need to rollover that file immediately.
Trying to figure out how much data we could write will resolve in
overflow of unsigned variable 'towrite' and this leads to segfault.
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

Otherwise we fail on 32bit with:

CC     logging/virtlogd-log_daemon_dispatch.o
logging/log_daemon_dispatch.c: In function 'virLogManagerProtocolDispatchDomainReadLogFile':
logging/log_daemon_dispatch.c:120:9: error: format '%zu' expects argument of type 'size_t', but argument 7 has type 'uint64_t' [-Werror=format]

Add virRotatingFileReader and virRotatingFileWriter objects
which allow reading & writing from/to files with automation
rotation to N backup files when a size limit is reached. This
is useful for guest logging when a guaranteed finite size
limit is required. Use of external tools like logrotate is
inadequate since it leaves the possibility for guest to DOS
the host in between invokations of logrotate.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>