ACCUMULO-3440 Bin assingment log messages

Don't spam log messages about assignments, but
also don't make huge log messages. Nice sized
log messages that are managable.
ACCUMULO-3435 Use RawLocalFileSystem

Restarting the nodes and expecting recovery
to actually working with the ChecksumFileSystem
just ain't gonna happen. Checksum errors prevent recovery
from happening which means the test can never finish.
RawLocalFilesystem ensures that we have the necessary
filesystem semantics for WALs.
Merge branch '1.6'