Docs: Update plugins.asciidoc to fix typo

Changed the name of the European Environment Agency (from European Environmental Agency)

Closes #6807
Add local node to cluster state
Today, the tribe node needs the local node so it adds it when it starts, but other APIs would benefit from adding the local node, also, adding the local node should be done in a cleaner manner, where it belongs, which is right after the discovery service starts in the cluster service
closes #6811
[STORE]: Make use of Lucene build-in checksums

Since Lucene version 4.8 each file has a checksum written as it's
footer. We used to calculate the checksums for all files transparently
on the filesystem layer (Directory / Store) which is now not necessary
anymore. This commit makes use of the new checksums in a backwards
compatible way such that files written with the old checksum mechanism
are still compared against the corresponding Alder32 checksum while
newer files are compared against the Lucene build in CRC32 checksum.

Since now every written file is checksummed by default this commit
also verifies the checksum for files during recovery and restore if
applicable.

Closes #5924

This commit also has a fix for #6808 since the added tests in
`CorruptedFileTest.java` exposed the issue.

Closes #6808