health_protocol: Adding action & message to ACK

When sending an ACK, let's keep both action & message to help sender
sorting what was the ACK for.
base.install: Fixing ident

Commit #9db2e46e4a4722b3121eb3293360c5aeb66536d7 was badly indented and lead to a travis failure.
Sorry for that.
health: Client informs server when benchmark starts

The client is now sending a specific message to inform when the
benchmark actually starts.
Add id/gid for SF in Centos 7.0