Low: all: constrain minimum when parsing certain internally generated integers

Since these values are all generated by Pacemaker, bounds-checking is just a
sanity check and shouldn't have any effect in practice.

A new internal API function, pcmk__scan_min_int(), is created to handle this
(replacing crm_parse_int() and its alias crm_atoi() for these purposes).

Examples include call IDs, exit statuses, and boolean values bounded to 0.