Merge July 2017 changes

DOC-606 : Document rocksdb_enable_ttl_read_filtering and associated debug variables

DOC-607 : Remove documentation for obsolete options rocksdb_max_background_compactions and rocksdb_max_background_flushes

http://jenkins.percona.com/view/5.7/job/mysql-5.7-param/1187/

http://jenkins.percona.com/view/5.7/job/mysql-5.7-param/1196/

https://github.com/percona/percona-server/pull/1918

Null cherry-picked commits in series :

1. fb-mysql-5.6.35/dcd30b0636fa7ad36fbf595d79c51e6daf9bd65b : renamed 2pc-mater test and temporarily disabled 2pc

2. fb-mysql-5.6.35/d73eb8a5715179e4ebecab217fdcdb348fb90dec : appended snapshot conflict error message

3. fb-mysql-5.6.35/1328f8fd89528a4e066d3e6c5bf0873a23d1beff : reset detailed error string for deadlock error

4. fb-mysql-5.6.35/841d41f48b151a8b8bc6ce5a85eeb603301b5c55 : Test cases for "Fix single delete use case for primary keys" (#655)

5. fb-mysql-5.6.35/8cef2f07ad105a7394ea039c0350d743560a9ad4 : fix varbinary-format-test nits

6. fb-mysql-5.6.35/744b757c5da3bf41778f3365fa63381e58218496 : added lock_wait_timeout and deadlock stats to rocksdb

7. fb-mysql-5.6.35/f1265d6f2072e2a2ab81e69a7c7b281301941dcc : Make rocksdb.ttl_primary test use error names instead of numeric codes

Merged upstream commits :

1. *DOC* fb-mysql-5.6.35/891a9115e3d16e1a2b2efab11eff1880eb69ce1e : [mysql-5.6][PR] implement query read filtering for tables with TTL enabled (primary k…

2. fb-mysql-5.6.35/20e993f5435391eb828cb653e953f759e2e960d1 : add test for prefix extractor override

3. fb-mysql-5.6.35/e0fe3a75c88f538ce98a3eb32c6c34aa819f536d : Fix single delete use case for primary keys

4. *DOC* fb-mysql-5.6.35/9131e508163c69d852337c23e54cfa8623cd8c15 : Remove obsolete options and start using max_background_jobs

5. fb-mysql-5.6.35/2e0ecaf5ce8cb4a1bb1debbe2269839d88de6f1d : Updating rocksdb submodule to latest to fix sysbench QPS reduction

6. fb-mysql-5.6.35/d52038f9911aac927874de94ad459d06d587e488 : Instrument ha_rocksdb::open with RocksDB perf context