Fix how module_common handles selevel (issue #4142)

Two fixes:

* parameter name is selevel, not serange.
* Fix split on selinux context to limit to max of 4 since the selevel
  may contain ':' characters.  This was fixed in
  selinux_default_context() and selinux_context().
zabbix inventory: print errors to stderr
Merge pull request #4145 from resmo/fix/zabbix-inventory-stderr

zabbix inventory: print errors to stderr