run_cli_handler: add no_rpcenv parameter

run_cli_handler: add no_rpcenv parameter

This can be used if a CLIHandler child class does not needs or wants
RPCEnv. E.g. this is the case with pve-cluster, as it's a dependency
of the package where RPCEnv resides (access-control), so this can be
set to avoid a implicit circular build dependency.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>