[ZabbixAPIEmulator] Simplify building JSON for events

This commit also fixes following bugs:

* The JSON doesn't include an event with id == eventid_till
* Too many events are returned when the limit value is too small

test_verifyEventsObtanedBySplitWay() will fail with this code because
both the test and the testee have some problems.
[ArmZabbixAPI] Fix a bug that a redundant event is requested on every requests

This commit will also fix an issue that a new event isn't fetched
until two or more new events are queued at Zabbix (issue #447),
but the test for it isn't added yet.
[ZabbixAPIEmulator] Simplify checking range of events
[ZabbixAPIEmulator] Avoid exceeding existing event ID
[ZabbixAPIEmulator] Fix a bug that wrong event ID is used on checking the range
[ZabbixAPIEmulator] Fix wrong checks for event range
[ZabbixAPIEmulator] Fix wong checks for number of events
[ZabbixAPIEmulator] More simplify building JSON for events
[ZabbixAPIEmulator] More simplify building JSON for events
[ZabbixAPIEmulator] Remove needless local variables
[ZabbixAPIEmulator] Use a readble variable name

i -> id
[ZabbixAPIEmulator] Fix a broken indent
[ZabbixAPIEmulator] Avoid duplicated search for zbxEventMap
[ZabbixAPIEmulator] Remove unused members
[ZabbixAPIEmulator] Use more readable names for members of PrivateContext

firstId -> firstEventId
lastId -> lastEventId
[ZabbixAPIEmulator] Move initializing apiHandlerMap to PrivateContext
[ZabbixAPIEmulator] Initialize all primitive members on reset()
[testArmZabbixAPI] Add a test for issue #447 (can't fetch one new event)
[ZabbixAPIEmulator] Fix a bug that setExpectedFirstEventId() uses a wrong member variable
[ZabbixAPIEmulator] Reset ParameterEventGet on every requests