BUG/MINOR: mworker: fix mworker-max-reloads parser

BUG/MINOR: mworker: fix mworker-max-reloads parser

Before this patch, when wrong argument was provided in the configuration for
mworker-max-reloads keyword, parser shows these errors below on the stderr:

[WARNING]  (1820317) : config : parsing [haproxy.cfg:154] : (null)parsing [haproxy.cfg:154] : 'mworker-max-reloads' expects an integer argument.

In a case, when by mistake two arguments were provided instead of one, this has
also triggered a buggy error message:

[ALERT]    (1820668) : config : parsing [haproxy.cfg:154] : 'mworker-max-reloads' cannot handle unexpected argument '45'.
[WARNING]  (1820668) : config : parsing [haproxy.cfg:154] : (null)

So, as 'mworker-max-reloads' is parsed in discovery mode by master process
let's align now its parser with all others, which could be called for this
mode. Like this in cases, when there are too many args or argument isn't a
valid integer we return proper error codes to global section parser and
messages are formated properly.

This fix should be backported in all stable versions.