snap ack should provide a summary of the assertions status

[Ryan Harper]

1. % lsb_release -rd
Description: Ubuntu 16.04.1 LTS
Release: 16.04

2. % apt-cache policy snapd
snapd:
  Installed: 2.16
  Candidate: 2.16
  Version table:
 *** 2.16 100
        100 /var/lib/dpkg/status
     2.15.2ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
     2.0.2 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages

3. % sudo snap ack my-assertions.txt
OK: system-user email: <email address hidden>
OK: account account-id: canonical
OK: account-key account-id: canonical
FAIL: snap-declaration snap-name: my-snap
OK: snap-declaration snap-name: hello
ACKed (4/5) assertions from my-assertions.txt

4. snap ack provides no feedback w.r.t which assertions were acked, how many, or the type.
It may be useful to extend the command to include --json like create-user which provides some feedback as to what was created (username, and number of ssh keys imported, etc).