Second round of ReqMgr CouchDB values fixes.

RequestSizeEvents - in majority of couch requests not defined, no references
    in the code (probably was at some point), should be removed from all Couch
    requests ; deprecated, injection fails will fail now if specified
RequestEventSize - deprecated, injection fails will fail now if specified,
    should be removed from all old Couch requests
SizePerEvent - must exist, parameter is mandatory, from Oracle is taken from
    reqmgr_request:REQUEST_EVENT_SIZE (mess that the above probably existed
    when someone was introducing SizePerEvent)
RequestSizeFiles - made mandatory, handled properly so that values are stored
    in Couch, on old requests values should be loaded from
    reqmgr_request:REQUEST_SIZE_FILES
RequestNumEvents - made mandatory, handled properly so that values are stored
    in Couch, on old requests values should be loaded from
    reqmgr_request:REQUEST_NUM_EVENTS
PrepID - made optional, properly stored in Couch, on old requests values
    should be loaded from reqmgr_request:PREP_ID

All unittests updated. reqmgr.py now contains checks for the above.
Database Oracle -> CouchDB migration/consistency scripts should implement the
above when migrating values.
Merge pull request #4500 from zdenekmaxa/reqmgr-fixing-database-consistency-issue-4388-2

Second round of ReqMgr CouchDB values fixes.