Quota is not preserved in snapshot INode

Quota feature is not preserved during snapshot creation, this causes INodeDirectory#metadataEquals to ALWAYS return true. Therefore, snapshotDiff will ALWAYS return the snapshot root as modified, even if the quota is set before the snapshot creation:

$ hdfs snapshotDiff /diffTest s0 .
Difference between snapshot s0 and current directory under directory /diffTest:
M	.