Fix current mapitest: module_zentyal

There were 2 issues executing `mapitest  --mapi-calls=ZENTYAL-ALL`:

* In 1863 `Administrator` user were being used (and normally this user won't have an openchange account), we can use the user from the profile which will have oc account acitvated for sure.
* 1872 test was giving sometime sigfaults because a bug (the original one) on nspi implementation
  * We were never setting `count` to 0, because `((ldb_res->count - r->in.pStat->NumPos) < 0)` is checking whether an `uint32_t` is < 0.
  * The test was sigfaulting because of `ldb_res->msgs[i+r->in.pStat->NumPos]` (NumPos is the faulty parameter we supply)
  * Besides we want to return an error instead of empty result and success result.
Really needed, no. But I'd prefer to be safe than sorry and think worst case scenario while testing. That means avoid giving pointers to data that doesn't belong to the current context (username is use from other mapitest). Again, no really needed here, but for me is better this way.