[#993] Register an entry container's configuration listeners only once it has opened

[vharseko]

Fixes #993.

The defect

EntryContainer registered itself and its two configuration managers as listeners of the backend
configuration from its constructor, and only close() takes them off again. open() caught
StorageRuntimeException alone, while it is declared to throw ConfigException and really does -
an index type the attribute has no matching rule for, an index protecting both its keys and its
values, and (the most reachable of the three) a VLV filter or sort order which does not parse.
Neither RootContainer.openEntryContainer nor openAndRegisterEntryContainers catches it either,
so the container is registered nowhere and nothing will ever call its close().

Two things in the report needed correcting, and both are in the analysis on the
issue: the
failure is not a NullPointerException - id2entry is assigned by the first statement of the
try - and it is more than five listeners, since every index the failed open got through
registered one of its own. What it costs is worse than an NPE:
ConfigurationHandler.replaceEntry asks every listener on the backend entry whether a change is
acceptable and a single false rejects the whole modify, so an abandoned container can veto a
change on the live backend; and past that gate the entry is already stored, so a failure from one
listener turns a change the live container applied into ERR_CONFIG_FILE_MODIFY_APPLY_FAILED.

The change

EntryContainer

• the five registrations move from the constructor to the end of a successful open(). A container
  which did not open is not one a configuration change has anything to be applied to, and nothing
  can reach it in between: open() is called before anything holds it.
• open() catches every failure rather than the storage ones alone, so a ConfigException also
  goes through close().
• each index is held in its map before it is opened. An attribute index registers its listener at
  the end of open() and a VLV index from its constructor, so the one being opened was not yet one
  close() could find - the hole the StorageRuntimeException catch already had.

RootContainer

• a failed open() gives back what it took: the entry containers it registered, its own listener,
  and the storage - the last only when this call is what opened it, since a read only root
  container is opened over the very storage instance the backend holds. Nothing else reclaims any
  of it: newRootContainer throws the instance away and BackendConfigManager releases the shared
  lock without calling closeBackend() for a backend which never opened, so a volume left open
  here is one no later attempt to enable that backend can take.
• openAndRegisterEntryContainers runs inside the write Storage.write may replay, so it gives up
  what a rolled back attempt registered before opening again. Without it an ordinary write-write
  conflict during startup fails the backend with ERR_ENTRY_CONTAINER_ALREADY_REGISTERED and
  leaves that attempt's containers registered - the same shape BackendImpl.changeBaseDNTrees
  already uses for the containers it opens inside a write.

The base DN path needs nothing of its own: a container whose open() throws now closes itself, so
the container changeBaseDNTrees never gets to put in created is reclaimed too.

Tests

FailedBackendOpenTest, five tests, each watched to fail first:

test	what it reported before the change
aBackendWhichFailsToOpenLeavesNothingRegistered	the root container, the entry container and both configuration managers left registered
anIndexWhichFailsToOpenLeavesNoListenerBehind	/dc=com,dc=b993/vlv.vlv1 left registered
aBackendWhichFailsToOpenGivesBackTheStorageItOpened	closes: expected 1, was 0
aRootContainerWhichCouldNotOpenTheStorageDoesNotCloseIt	guards the storage a read only container did not open
aReplayedOpenLeavesOneSetOfEntryContainers	An entry container named 'dc=com,dc=b993' is alreadly registered

Run green with them: PDBTestCase 35/35, EncryptedPDBTestCase 35/35, ReplayedConfigChangeTest
12/12, PDBStorageTest 10/10, OnDiskMergeImporterTest 29/29, PersistentCompressedSchemaTest,
DN2IDTest, StateTest, ID2EntryTest, ID2ChildrenCountTest, BulkCursorTest,
DefaultIndexTest.