Convert rsyslog config to RainerScript-based filters

While reviewing I5e8ea2b, Faidon pointed out that the mixing of
selectors and RainerScript filters in the rsyslog config was confusing.

I couldn't find RainerScript syntax for $outchannel. I also did not
change the `@` syslog forwards to actions as that requires providing the
host and port separately.

Change-Id: I03be7b53608aab0711a6d51cd8b476f3c3604950