Ensure find is installed on MariaDB containers

wsrep_sst_mariabackup script that syncs data for members joining cluster
leverages `find` util heavily. While Ubuntu LXC image seems to contain
it out of the box, EL does miss it. While we do not see any issues due
to missing `find` on modern MariaDB, script still apparently relies on
it's existance, though can handle cases when it's not present.
Still let's ensure it's present, as it feels playing important role.

Change-Id: Ia10a9ab589275f18ff2c92a21cd2ff9aeac07567
(cherry picked from commit 64b54f2458)

vars/debian.yml

@@ -50,6 +50,7 @@ _galera_mariadb_server_package: "mariadb-server"
 # the preseed task and the service startup control used when installing
 # mariadb-galera-server and galera.
 galera_server_mariadb_distro_packages:
+  - findutils  # "find" is used by wsrep_sst_mariabackup script
   - libmariadb-dev
   - mariadb-client
   - mariadb-backup

vars/redhat.yml

@@ -25,6 +25,7 @@ _galera_gpg_keys:
 _galera_disable_privatedevices: yes
 
 galera_server_required_distro_packages:
+  - findutils  # "find" is used by wsrep_sst_mariabackup script
   - gnupg2
   - libaio
   - libstdc++