Zabbix

A.F....PS. [ZBXNEXT-4428] optimized SNMP discovery and data collection, added GetBulk support

Merge in ZBX/zabbix from feature/ZBXNEXT-4428-6.3-b to master

* commit 'f021e805d85b0518762f028009ed47cf98d4d89e': (92 commits)
  .......... [ZBXNEXT-4428] removed cases that do not work without mibs downloaded
  .......... [ZBXNEXT-4428] fixed schema
  .......PS. [ZBXNEXT-4428] fixed dbpatch
  .......... [ZBXNEXT-4428] removed redundant schema.inc.php
  .......... [ZBXNEXT-4428] added changelog
  .......PS. [ZBXNEXT-4428] added testcases for multiline hex string
  .......PS. [ZBXNEXT-4428] fixed bulkwalk output
  .......... [ZBXNEXT-4428] added test case for multiline hex string
  .......PS. [ZBXNEXT-4428] fixed parsing of multiline hex strings
  ..F....... [ZBXNEXT-4428] fixed undefined index in item test
  .......... [ZBXNEXT-4428] fixed missing fields in autotests
  .......PS. [ZBXNEXT-4428] moved root bulkwalk implementation to separate function to avoid retry code
  .......PS. [ZBXNEXT-4428] retrieve single instance oids with GET
  A......... [ZBXNEXT-4428] fixed max_repetitions field not mandatory in host inerface API
  .......PS. [ZBXNEXT-4428] fixed end-of-tree problem
  .......PS. [ZBXNEXT-4428] make end-of-tree output like in snmpwalk, fixed crash
  ..F....... [ZBXNEXT-4428] added validation to item test; fixed code style
  .......PS. [ZBXNEXT-4428] fixed snmp bulk walk parameter processing
  .......PS. [ZBXNEXT-4428] invalid max_reps should fail earlier
  .......PS. [ZBXNEXT-4428] removed hardcoded default value for max_reps
  ...