[AMBARI-25671] Moved cache deletion at the end in delete flow

[shubhamod]

What changes were proposed in this pull request?

According to current delete flow, we are deleting the cache data first and then deleting data from db. But if due to anycase like Rollback exceptions , we delete the data from cache but data in DB is rollbacked. Due to this when again we try to delete the host data, it throws hostNotFound since it takes this check from cache given below.

Set clusters = getHostClustersMap().get(hostname);
if (clusters == null) {
throw new HostNotFoundException(hostname);
}

if (!getHostsByName().containsKey(hostname)) { throw new HostNotFoundException("Could not find host " + hostname); }

So even though data is not actually deleted from DB , we still wont delete from DB because of this. The current way is to restart ambari server which fills up the cache again and then it works fine, but until that, we wont be able to delete anything for this hostName.

How was this patch tested?

(Please explain how this patch was tested. Ex: unit tests, manual tests)
(If this patch involves UI changes, please attach a screen-shot; otherwise, remove this)

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