Split Travis unittests Job

Summary:
  - Update Makefile check_some command to run a subset of the tests
  - Update travis config to split the unittests job into 2 jobs
     -- job testing db_test, db_test2
     -- job testing the rest of the unittests

Test Plan:
Run the new travis.yml on my own branch
https://travis-ci.org/facebook/rocksdb/builds/122691453

Reviewers: kradhakrishnan, yhchiang, sdong, andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D56673

.travis.yml

@@ -11,8 +11,13 @@ addons:
       sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.6']
       packages: ['clang-3.6' , 'zlib1g-dev', 'libbz2-dev', 'libsnappy-dev', 'curl']
 env:
-  - JOB_NAME=unittests
+  # Run all tests before db_block_cache_test (db_test, db_test2)
+  - JOB_NAME=unittests ROCKSDBTESTS_END=db_block_cache_test
+  # Run all tests starting from db_block_cache_test (db_block_cache_test, db_iter_test, ...)
+  - JOB_NAME=unittests ROCKSDBTESTS_START=db_block_cache_test
+  # Run java tests
   - JOB_NAME=java_test
+  # Build ROCKSDB_LITE
   - JOB_NAME=lite_build
 
 install:
@@ -32,7 +37,7 @@ before_script:
   - ulimit -n 2000 || true
 
 script:
-  - if [[ "${JOB_NAME}" == 'unittests' ]]; then OPT=-DTRAVIS V=1 make -j4 check; fi
+  - if [[ "${JOB_NAME}" == 'unittests' ]]; then OPT=-DTRAVIS V=1 make -j4 check_some; fi
   - if [[ "${JOB_NAME}" == 'java_test' ]]; then OPT=-DTRAVIS V=1 make clean jclean rocksdbjava jtest; fi
   - if [[ "${JOB_NAME}" == 'lite_build' ]]; then OPT="-DTRAVIS -DROCKSDB_LITE" V=1 make -j4 static_lib; fi
 notifications:

Makefile

@@ -354,7 +354,14 @@ TESTS = \
 	ldb_cmd_test \
 	iostats_context_test
 
-SUBSET :=  $(shell echo $(TESTS) |sed s/^.*$(ROCKSDBTESTS_START)/$(ROCKSDBTESTS_START)/)
+SUBSET := $(TESTS)
+ifdef ROCKSDBTESTS_START
+        SUBSET := $(shell echo $(SUBSET) | sed 's/^.*$(ROCKSDBTESTS_START)/$(ROCKSDBTESTS_START)/')
+endif
+
+ifdef ROCKSDBTESTS_END
+        SUBSET := $(shell echo $(SUBSET) | sed 's/$(ROCKSDBTESTS_END).*//')
+endif
 
 TOOLS = \
 	sst_dump \