Problem was that the mix of handlers was not consistent between
CREATE and ALTER

changed so that it works like:
    - All partitions must use the same engine
      AND it must be the same as the table.
    - if one does NOT specify an engine on the table level
      then one must either NOT specify any engine on any
      partition/subpartition OR for ALL partitions/subpartitions

Note: that after a table have been created, the storage engine
is specified for all parts of the table (table/partition/subpartition)
and so when using alter, one does not need to specify it (unless one
wants to change the storage engine, then one have to specify it on the
table level)