[sheepdog] sheepdog test_hash failure

[Ruoyu]

Hi Robin,

Once I apply your patch "sheep/md: change the method of generating 
vnodes in md", sheepdog unit test will be failure.
Could you please help to fix it?

Run steps:

git checkout 3db9979bfc0554a1d6758781eebbdcb421fa8fca
./configure --enable-unittest
make check

Output:

PASS: test_vdi
PASS: test_cluster_driver
FAIL: test_hash

============================================================================
Testsuite summary for sheepdog 0.8.0_157_g8b64f28
============================================================================
# TOTAL: 3
# PASS:  2
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0
============================================================================
See tests/unit/sheep/test-suite.log
Please report to sheepdog at lists.wpkg.org
============================================================================