Fix improper error handling

[crd1985]

Description

This PR closes #292, closes #293.

Fixes the policy of error reporting of Wazuh API. Instead of returning the full description of errors in the API responses, it writes them in the api.log file when debug mode is enabled.
This avoids showing private filepaths or any other information useful for an attacker.

Tests performed

Sent some request to an api in debug mode.

• Try internal error on console and see the api.log

# curl -u foo:bar "localhost:55000/cluster/node045/stats?pretty"{
   "error": 1000,
   "message": "Internal error"
}

## In api.log file...
WazuhAPI 2019-01-24 11:06:38 foo: totals() got an unexpected keyword argument 'node_id'
WazuhAPI 2019-01-24 11:06:38 foo: [::ffff:127.0.0.1] GET /cluster/node045/stats?pretty - 200 - error: '1000'.

• Try other errors

# curl -u foo:bar "localhost:55000/agents/groups/default/files/passwd?pretty"
{
   "error": 1006,
   "message": "File/directory does not exist"
}

## In api.log file...
WazuhAPI 2019-01-24 11:14:42 foo: File/directory does not exist: /var/ossec/etc/shared/default/passwd
WazuhAPI 2019-01-24 11:14:42 foo: [::ffff:127.0.0.1] GET /agents/groups/default/files/passwd?pretty - 200 - error: '1006'.

# curl -u foo:bar "localhost:55000/agents/groups/perere?pretty"
{
   "error": 1710,
   "message": "The group does not exist"
}

## In api.log file...
WazuhAPI 2019-01-24 11:15:31 foo: The group does not exist: perere
WazuhAPI 2019-01-24 11:15:31 foo: [::ffff:127.0.0.1] GET /agents/groups/perere?pretty - 200 - error: '1710'.

# curl -u foo:bar -k -X POST -d '{"name":"NewHost","ip""10.0.0.9"}' -H 'Content-Type:application/json' "http://127.0.0.1:55000/agents?pretty"
{"error":"614","message":"Invalid request. Body is not correct."}

## In api.log file...
WazuhAPI 2019-01-24 11:23:11 foo: [::ffff:127.0.0.1] POST /agents?pretty - 400 - error: '614'.