Enhancement: abc import should report indexing failures

`abc import` logs currently don't show the number of records that failed to index. This behavior can be easily supported as the underlying bulk API reports the failures.

A sample output line for this can be:

- When there are failures: `10 out of 4654 total records failed to index`
- When indexing succeeds: `4654 total records indexed`.

Note: We only report total records when a data source import is divided across multiple bulk requests. We should correspondingly also report total failures per import command.

**Version Info**:
Version: 1.0.0-alpha.0
Variant: !oss
Go version: go1.11.10
OS: linux
Arch: amd64