[DOCS] Fix link to statsd plugin

Fixes #4128
Just filter test jar and not the main jar file
s/AbstractIntegrationTest/ElasticsearchIntegrationTest
close transport client to wait for ongoing samples
the transport client should not be executing at the same time as sampling happens, so connection open/close logic will be properly maintained
upgrade to Netty 3.8.0
Change default store impl to mmapfs on 64bit Linux.
Fixes #4134
[DOCS] Update store docs to indicate mmapfs is now the default on 64-bit Linux
Lazily fill CharTermAttribute if needed in CompletionTokenStream

This adds a delegate to CharTermAttributeImpl to be compatible
with the Percolator that needs a CharTermAttribute. Yet compared
to CharTermAttributImpl we only fill the BytesRef with UTF-8 since
we already have it and only if we need to convert to UTF-16 we do it.

Closes #4028