Use BufferedOutputStream for deflater

Testing Done:
./gradlew build

Microbenchmark with a scheduler backup from my production environment.

Before:
# Deflater.DEFAULT_COMPRESSION
# (No BufferedOutputStream)
# DeflaterOutputStream(512B)
deflate: 16664ms
total:17219ms
compression ratio: 647270930/92690409 = 698.31%

After:
# Deflater.DEFAULT_COMPRESSION
# BufferedOutputStream(256KiB)
# DeflaterOutputStream(256KiB)
deflate: 11807ms (4857ms speedup)
total: 12379ms (4840ms speedup)
compression ratio: 647270930/92690409 = 698.31% (0% improvement)

Bugs closed: AURORA-722

Reviewed at https://reviews.apache.org/r/26012/
Renaming update to beta-update in client v2

Bugs closed: AURORA-757

Reviewed at https://reviews.apache.org/r/26089/
Adding JobUpdateRequest validation.

Bugs closed: AURORA-649

Reviewed at https://reviews.apache.org/r/25481/
Prevent initial ZK timeouts from killing the executor.

In addition, prevent uncaught exceptions from killing the executor.