mysql_install_db doesn't properly grant proxy privileges to all default root user accounts

mysql_install_db is supposed to grant proxy privileges to the default root user accounts. However, it currently only does that for a subset of the default root user accounts. The specific user accounts depends on the specific version of MariaDB.

Here is the relevant code in all versions:

10.1 - https://github.com/MariaDB/server/blob/mariadb-10.1.43/scripts/mysql_system_tables_data.sql#L60
10.2 - https://github.com/MariaDB/server/blob/mariadb-10.2.29/scripts/mysql_system_tables_data.sql#L63
10.3 - https://github.com/MariaDB/server/blob/mariadb-10.3.20/scripts/mysql_system_tables_data.sql#L48
10.4 - https://github.com/MariaDB/server/blob/mariadb-10.4.10/scripts/mysql_system_tables_data.sql#L52

In 10.1, 10.2, and 10.3, it grants the proxy privilege to the following user accounts:

• root@'localhost'
• root@current_hostname

In 10.1, 10.2, and 10.3, this means that the following user accounts are missing the grant:

• root@'127.0.0.1'
• root@'::1'

In 10.4, it grants the proxy privilege to the following user accounts:

• root@current_hostname

In 10.4, this means that the following user accounts are missing the grant:

• root@'localhost'
• root@'127.0.0.1'
• root@'::1'