WL#10886: Add/Extend mtr tests for Replication/GR for roles

A role is a named collection of privileges. One can grant roles, grant to roles,
create roles, drop roles, and decide what roles are applicable ("enabled")
during a session.

Also there are mandatory-roles, ref WL#924.

In Replication we must add/modify tests to ensure that Roles are replicated as
expected and also create a suite for the same, to ensure replication and group
replication users existing/new can use this feature.

FR1. Test must verify that ROLES are replicated successfully.

FR2. Test must verify that ROLES on replication users used in 'CHANGE MASTER TO' 
work as expected for RPL/GR.

FR3. Test must verify that Activating the role by 'ALTER USER' is successful on 
both master/slave and GR members.

FR4. Test must verify execution of GR/RPL commands is successful by the user when 
different privileges are granted by roles.

This worklog implements test to verify following scenarios in GR:

1.Verify that ROLES are replicated successfully.
   1.1 Create role, user on server1.
   1.2 Grant privileges to roles and grant roles to users.
2.Verify execution of GR commands is successful by the user when different
privileges are granted by roles.
   2.1 Error as user does not have privilege to execute command.
   2.2 Assign SYSTEM_VARIABLES_ADMIN privilege to user by enabling the role
       and test that command is executed successfully.
3.Verify that ROLES on replication users used in 'CHANGE MASTER TO' work
   as expected for GR.
   3.1 Error in START GR as master_user used in CHM does not have privilege.
   3.2 Assign REPLICATION_SLAVE privilege to user by enabling the role and
       test that start group_replication succeeds.
4.Verify that Activating the role by 'ALTER USER' is successful on all GR members.

This worklog modified test to verify following scenario in core replication:

1. Verify that ROLES on replication users used in 'CHANGE MASTER TO' work
   as expected.
   1.1 Error in START SLAVE as master_user used in CHM does not have privilege.
   1.2 Assign REPLICATION_SLAVE privilege to user by enabling the role and
       test that START SLAVE succeeds.