Add support for running snowflake migrations

Add coreutils to build-harness (#116)

**Why**
For running snowflake migrations on supernova deploys need suppport
for relative dates in date - this is provided by coreutils:
```
bash-5.0# date -d "last monday -7 days" +%Y-%m-%d
2021-03-29
```

Also put all the packages into one apk command instead of separate ones.
And deleted obsolete line to cleanup apk cache, since we are running apk
with --no-cache.

**Testing**
Tested locally