Post-fixes for "Rename plugin rocksdb_se to rocksdb"

- Also rename plugin's config file
- And fix unit test's CMakeLists.txt

debian/mariadb-plugin-rocksdb.install

-etc/mysql/conf.d/rocksdb_se.cnf etc/mysql/mariadb.conf.d
+etc/mysql/conf.d/rocksdb.cnf etc/mysql/mariadb.conf.d
 usr/lib/mysql/plugin/ha_rocksdb.so
 usr/bin/mysql_ldb
 usr/bin/sst_dump

storage/rocksdb/unittest/CMakeLists.txt

-IF (WITH_ROCKSDB_SE_STORAGE_ENGINE)
+IF (TARGET rocksdb)
   INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR}/include ${CMAKE_SOURCE_DIR}/zlib
                       ${CMAKE_SOURCE_DIR}/unittest/mytap
     ${CMAKE_SOURCE_DIR}/rocksdb/third-party/gtest-1.7.0/fused-src