Standardize snapshot CLI output

[drewbanin]

Fixes #1768

Output:

$ dbt snapshot
Running with dbt=0.15.0-a1
Found 2 models, 5 tests, 1 snapshot, 0 analyses, 130 macros, 0 operations, 2 seed files, 1 source

22:36:19 | Concurrency: 8 threads (target='dev')
22:36:19 |
22:36:19 | 1 of 1 START snapshot snapshots.my_snapshot... [RUN]
22:36:19 | 1 of 1 OK snapshotted snapshots.my_snapshot... [INSERT 0 0 in 0.20s]
22:36:19 |
22:36:19 | Finished running 1 snapshot in 0.40s.

[beckjake]

lgtm!