Client acks messages sent between services on the client.

On the client, when service A sends a message to service B (on the same client), the fleetspeak client will send an ACK to the server.

This results in the following logs:

```
W0901 16:26:11.600130 25931 manager.go:209] system: Temporary error processing message 97e7d6d3e241aaf07944a169d5601d2d39ea62e58b22dfb39576fe015feefe90, will retry: unable to retrieve messages to ack: sql: no rows in result set
W0901 16:26:11.600792 25931 manager.go:209] system: Temporary error processing message 72739dbc6cbfe90879fdc89bcd9f20b05b706e21471a83a402db7f32349636b7, will retry: unable to retrieve messages to ack: sql: no rows in result set
W0901 16:26:12.802231 25931 manager.go:209] system: Temporary error processing message 936cddf4fea77cc8525cfa9273d5f8e65a158abd9e73cd1ae9bc21d9a0e9ce10, will retry: unable to retrieve messages to ack: sql: no rows in result set
W0901 16:26:13.099519 25931 manager.go:209] system: Temporary error processing message fa734a308287b58bf618fa768b54108e54a69e0e81162adadefd7f3b8eeb3193, will retry: unable to retrieve messages to ack: sql: no rows in result set
W0901 16:26:14.601890 25931 manager.go:209] system: Temporary error processing message 129c170732eae60c1738ea92caa4893649b4238a279025e4af802f877bd6109b, will retry: unable to retrieve messages to ack: sql: no rows in result set
W0901 16:26:14.899605 25931 manager.go:209] system: Temporary error processing message e707f680871c375adea0dd13d20c2829b83eab1ae3c6ccd59b7c7d9bf7431f51, will retry: unable to retrieve messages to ack: sql: no rows in result set
W0901 16:26:15.499319 25931 manager.go:209] system: Temporary error processing message 47812d87eae92816856bd4101ffe5cdeb58f533eca7ddbaf49d0fbd38e278c25, will retry: unable to retrieve messages to ack: sql: no rows in result set
W0901 16:26:16.699828 25931 manager.go:209] system: Temporary error processing message 33a77e4c31b6ea3679c0fafc1c40c8615078e32d6eec73f72c8d0a5c6bf2f0a4, will retry: unable to retrieve messages to ack: sql: no rows in result set
```

The `MessageAckData` contains empty message IDs.

```
{ # (null) size=120B
tag1_message: { # (null) size=0B
} # tag1_message[0]
tag1_message: { # (null) size=0B
} # tag1_message[1]
tag1_message: { # (null) size=0B
} # tag1_message[2]
tag1_message: { # (null) size=0B
} # tag1_message[3]
tag1_message: { # (null) size=0B
} # tag1_message[4]
[...]
```

No Acks should be sent in this case, special handling should be implemented around here:

https://github.com/google/fleetspeak/blob/616a079d4c55e4637574ddda1804ce36d68cde18/fleetspeak/src/client/services.go#L292