20610: Adds 'balancer' role to the installer scripts.

20610: Adds 'balancer' role to the installer scripts.

Also, fixes a salt bootstrap issue dur to the fact that as of today, the 3004
version is no longer considered 'stable'.

Also, changes the way we use SSH so that no envvars are forwarded to remote
hosts, to avoid having 'setlocale' warnings mixed with salt cmd.run
outputs when using Debian distros to run the installer. This avoids issues
on the first run, before salt configures the remote node's locale.

Arvados-DCO-1.1-Signed-off-by: Lucas Di Pentima <lucas.dipentima@curii.com>