Add MySQL configs and log-files to the diagnostic snapshot

This will be added to the diagnostic snapshot:
 - /etc/mysql/*
 - /var/log/mysql/*
 - commands/mysql_resources.txt
The file commands/mysql_resources.txt will contain the listing files
from the /var/lib/mysql/ and /var/run/mysqld/ directories.

Change-Id: Iddaa9e0d51a02e0d2962dc797c4c1d1cd35b949e
Closes-Bug: #1550984
(cherry picked from commit 9d810891ff)

nailgun/nailgun/settings.yaml

@@ -856,6 +856,13 @@ DUMP:
       - type: command
         command: "for ns in $(ip netns list); do echo Namespace: ${ns}; ip netns exec ${ns} netstat -anp; done"
         to_file: netstat_ns.txt
+      - type: dir
+        path: /etc/mysql
+      - type: dir
+        path: /var/log/mysql
+      - type: command
+        command: "ls -la /var/lib/mysql/ /var/run/mysqld/"
+        to_file: mysql_resources.txt
 
     slave:
       hosts: []