osd: bluestore: improve fs-type verification and tidy up

[xiexingguo]

No description provided.

[xiexingguo]

Dropped those changes you disagree with and fixed the rest. Also make sure it passed my local test(script: rm -rf c store_test_temp_dir && make ceph_test_objectstore && CEPH_ARGS="--log-file c --debug-bluestore 20 --no-log-to-stderr" ./ceph_test_objectstore), below is the result:

2016-02-23 20:27:35.617754 7f37362794c0 -1 WARNING: experimental feature 'rocksdb' is enabled
Please be aware that this feature is experimental, untested,
unsupported, and may result in data corruption, data loss,
and/or irreparable damage to your cluster.  Do not use
feature with important data.

==> rm -r store_test_temp_dir
[       OK ] ObjectStore/StoreTest.SetAllocHint/3 (111 ms)
[----------] 160 tests from ObjectStore/StoreTest (3068328 ms total)

[----------] Global test environment tear-down
[==========] 160 tests from 1 test case ran. (3068328 ms total)
[  PASSED  ] 160 tests.