schema: Make writing indices flag an enum for a new state

schema: Make writing indices flag an enum for a new state

In schema_load_init, we find that the writing of indices is not locked
in any way. This leads to race conditions. To resolve this, we need to
have a new state (SCHEMA_COMPARE) which can report to the caller that we
need to open a transaction to write the indices.

Signed-off-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>