[fuel][doc] bad command example in operations guide for galera cluster autorebuild

[Marcin Iwinski]

Command examples in section "HowTo: Enable/Disable Galera Cluster Autorebuild Mechanism" [1] doesn't actually work.

Section describing how to check GTID and SEQNO across all nodes saved in Corosync CIB says that the following command should be used:
cibadmin --query --xpath "//nodes/*/*/nvpair[@name=\"gtid\"]"

This query however doesn't work.

~# cibadmin --query --xpath "//nodes/*/*/nvpair[@name=\"gtid\"]"
Call cib_query failed (-6): No such device or address

same bad query is used also in a description how to remove all GTIDs and SEQNOs from Corosync CIB (last example of this section).

[1] https://docs.mirantis.com/openstack/fuel/fuel-6.1/operations.html#howto-enable-disable-galera-cluster-autorebuild-mechanism