vshCmddefHelp: Refactor and fix printing of help for _STRING/_INT arguments

vshCmddefHelp: Refactor and fix printing of help for _STRING/_INT arguments

Use the new flags to do the decisions which will also fix the case when
an _INT option is required but non-positional.

This fixes the help for the 'timeout' argument of 'daemon-timeout'
virt-admin command:

     SYNOPSIS
  -    daemon-timeout <timeout>
  +    daemon-timeout --timeout <number>

[...]
     OPTIONS
  -    [--timeout] <number>  number of seconds the daemon will run without any active connection
  +    --timeout <number>  number of seconds the daemon will run without any active connection

Resolves: https://issues.redhat.com/browse/RHEL-25993
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>