test_installutils: run gpg-agent under a specific SELinux context
    
    system_u:system_r:init_t:s0 cannot execute gpg=agent when SELinux is in
    enforcing mode. Use SELinux context that allows this execution:
    system_u:system_r:initrc_t:s0 and wrap the whole execution into a bash
    run to make sure init_t -> initrc_t transition.
    
    Fixes: https://pagure.io/freeipa/issue/8699
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>