Add not so neat set_timeout call to make testMgm work

Index: ndb-work/storage/ndb/include/mgmapi/mgmapi.h
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storage/ndb/include/mgmapi/mgmapi.h:
  WL#3704 mgmapi timeouts: add ndb_mgm_set_timeout(h,ms)
storage/ndb/src/mgmapi/mgmapi.cpp:
  WL#3704 mgmapi timeouts: add ndb_mgm_set_timeout(h,ms)
storage/ndb/test/ndbapi/testMgm.cpp:
  WL#3704 mgmapi timeouts: add ndb_mgm_set_timeout(h,ms)