* [FLINK-10436] Add ConfigOption#withFallbackKeys

* [hotfix] correct javadoc

* [FLINK-10436] Code quality improvement

Move initialization logic out of the ZooKeeperSubmittedJobGraphStore constructor.

This addresses CVE-2018-11771.

Bump the jython dependency because of a security issue.

This closes #7287.

return null

[FLINK-10555] tests are all of BlobServer initialization, also remove already covered tests

This closes #6849.

After introducing CompositeTypeSerializerSnapshot, the
CompositeSerializerSnapshot has been reworked to only deal with concerns
of delegating reading and writing of the nested serializers' snapshots.
It no longer deals with resolving the final compatibility result for the
outer composite serializer.

Therefore, it is renamed properly as NestedSerializersSnapshotDelegate,
and also annotated as an internal class, since we want users to use the
more powerful CompositeTypeSerializerSnapshot instead.

This closes #7422.

[hotfix] [core] Assert current serializer snapshot is expected snapshot class in TypeSerializerSnapshotMigrationTestBase

This strengthens the test base to make use of the provided snapshot
class in the test specifications, to assert that serializers are really
using the expected classes for their current serializer snapshots.

[FLINK-11073] [core] Replace GenericArraySerializerConfigSnapshot with new GenericArraySerializerSnapshot

The CompositeTypeSerializerSnapshot encapsulates logic for handling
writing, reading, and deriving final compatibility results for composite
serializers that have multiple nested serializers as well as some
static outer configuration (e.g. type class in the
GenericArraySerializer).

his base class has its own versioning for the format in which it writes
the outer snapshot and the nested serializer snapshots. The version of
the serialization format of this based class is defined
by getCurrentVersion(). This is independent of the version in which
subclasses writes their outer snapshot, defined by
getCurrentOuterSnapshotVersion().

This means that the outer snapshot's version can be maintained only
taking into account changes in how the outer snapshot is written.
Any changes in the base format does not require upticks in the outer
snapshot's version

[FLINK-11280] [state backends, tests] Do not set current key before restore in TtlStateTestBase tests

Prior to this commit, the composite key builder was created in the
constructor of the RocksDBKeyedStateBackend. The creation of the builder
requires providing a key serializer.

This is problematic, because the key serializer may be reconfigured
during the restore phase, therefore invalidating the key serializer used
by the composite key builder.

This commit resolves this by lazily creating the composite key builder
only after the restore phase, which would be the point-in-time when we
are certain the key serializer will no longer be changed and is final.