ReqMgr delete request from CouchDB

Delete request when called deleteRequest() method from Oracle
as well as from CouchDB.
Passes all ReqMgr tests locally, however doens't work because
of a bug in CouchDB low level document delete: #4403 originating
from #4396 - once this low level problem is resolved, it
shall be fine. Tests added into reqmgr.py

Fixes #4289
Merge pull request #4423 from zdenekmaxa/reqmgr-delete-requests-from-couch

ReqMgr delete request from CouchDB