Fix race condition in XML parser

[vikman90]

We detected that, in particular cases, the Windows agent shows this error on startup:

2018/04/17 23:42:08 ossec-agent: INFO: (4102): Connected to the server (192.168.74.2:1514).
2018/04/17 23:42:08 ossec-agent: ERROR: (1226): Error reading XML file 'ossec.conf': XMLERR: Element not opened. (line 2).
2018/04/17 23:42:08 ossec-agent: ERROR: (1226): Error reading XML file 'ossec.conf': XMLERR: Attribute '<ossec_config' has no value. (line 8).
2018/04/17 23:42:08 ossec-agent: INFO: Received exit signal.
2018/04/17 23:42:08 ossec-agent: INFO: Exiting...
2018/04/17 23:42:08 rootcheck: CRITICAL: (1202): Configuration error at 'ossec.conf'. Exiting.

(...)

2018/04/17 23:53:12 ossec-agent: INFO: (4102): Connected to the server (192.168.74.2:1514).
2018/04/17 23:53:12 ossec-agent: ERROR: (1226): Error reading XML file 'ossec.conf': XMLERR: Element not opened. (line 11).
2018/04/17 23:53:12 wazuh-modulesd:ciscat: INFO: Module disabled. Exiting...
2018/04/17 23:53:12 ossec-agent: INFO: Received exit signal.
2018/04/17 23:53:12 ossec-agent: INFO: Exiting...

This bug is due to a race condition between the Syscheck and the main thread: the former loads the Syscheck settings at the same time as the latter reads the modules. This produces a race condition in the XML parser since it uses some global variables.

This PR moves such variables to the XML structure, but does not change the algorithm.

[albertomn86]

Tested in Windows Server 2016 👍