[TD-307]

This patch adds more error handling code:
1. In dnodeAllocateWqueue(), if the allocation of pWorker fails, any
allocated memory should be unwound and returns a NULL queue. This is
a better function contract where either all allocation succeeds or none
succeeds.
2. In vnodeOpen(), handle allocation failure for pVnode.

This patch refactors the initialization and cleanup path of dnode
with a table driven method. This fixes the following issues:

1. Before the patch, if dnodeInitRead() fails, the cleanup path
also runs dnodeCleanupWrite(), which will free wWorkerPool.writeWorker that's
never allocated. (The code before this patch will not crash though, because
wWorkerPool is zero-initialized global variable and therefore the
accidental free will be a nop).
2. In general the order of calling cleanup function should be reverse
to the order of calling init function, but this is not the case prior
to this patch (see dnodeCleanupMnode() and dnodeCleanupMgmt()).

* Bonus fix
This patch also fixes a missing free for readPool.readWorker.

* Testing
I plan to run the test script ./test-all.sh, but was not able to do so.
Is there a reference somewhere I can look up?

* Description
This patch fixes enablement of TSDB_MOD_MGMT module, which was
incorrectly assign to 'name' variable.

* Testing
Compile the code. Feel free to suggest more testing that needs to
be done. Given that 'tsModule' is zero initialized, I don't think
there's any functional difference for this patch.