Add qdevice membership parsing and metric label

[MalloZup]

Fix #170

There is only one special case, we might need to handle:

ha_cluster_corosync_member_votes{local="false",node="Qdevice",node_id="0",qdevice=""} 1

when the qdevice is active

Quorum information
------------------
Date:             Thu Jul 16 12:40:44 2020
Quorum provider:  corosync_votequorum
Nodes:            2
Node ID:          1
Ring ID:          1/139
Quorate:          Yes

Votequorum information
----------------------
Expected votes:   3
Highest expected: 3
Total votes:      3
Quorum:           2  
Flags:            Quorate Qdevice 

Membership information
----------------------
    Nodeid      Votes    Qdevice Name
         1          1    A,V,NMW nfs01 (local)
         2          1    A,V,NMW nfs02
         0          1            Qdevice

the table qdevice is empty so we create an empty metric.

I was thinking in order to avoid an empty metric we should populated the label qdevice with qdevice for indicating that it is the qdevice.

@gao-yan @nick-wang let me know what do you think

[stefanotorresi]

I was thinking in order to avoid an empty metric we should populated the label qdevice with qdevice for indicating that it is the qdevice.

Well, it's not really empty, you can see it's the Qdevice from the name! I don't think this is that special, after all.

[stefanotorresi]

thanks Dario!

[MalloZup]

thx