feat(bigtable/cbt): cbt 'import' cmd to parse a .csv file and write to CBT

[markduffett]

Add 'import' command to 'cbt' and unit/emulator tests

• parses and imports .csv files only for now
• should be accompanied/shortly followed by a tutorial + sample.csv
• csv file formatting assumes a column family row is present unless flag 'column-family' is set, then it will use that family for all columns
• configurable batch-size(500 rows) and worker threads(1) defaults

Runtime expectations:
2MB file with 12588 rows

• 1s with 20 workers, 5s with the default 1

190MB file in 4s @ 47.5MB/s when using 'batch-size=5' 'workers=20'

• 50%+ of 1 Node/tabletservers' CPU
• 1288 rows, 1000 cols, 5kB data populated in 3% of cells
• 200MB/s+ depending on mutation size and number of CBT nodes

[crwilcox]

Looks like another linter error showed up.

bigtable/cmd/cbt/cbt_test.go:384:10: if block ends with a return statement, so drop this else and outdent its block (move short variable declaration to its own line if necessary)

Also, if you'd like, the script that is running is /internal/kokoro/vet.sh. You can get pretty close by running golint ./..., gofmt, goimports, though there are a few linter instances where we ignore failures (linting was added later)

[crwilcox]

nit: I think more typically the tests just catch this via an OR or two separate conditionals, collapsing this a bit? I may be missing nuance here

[markduffett]

This case would allow continuation since the fail is expected, but we don't want to do any comparisons below. It can't be paired with any of the above because they add errors were as this is expected.

I can put the if err == nil {t.Error} inside the tc.fail block, just wasn't sure if go-style preferred the nested ifs.

if tc.fail {
    if err == nil {
	t.Errorf("parseImportArgs() did not fail. input:%+v, error:%s", tc, err)
    }
    continue
}

[crwilcox]

this to me seems like we are trying to check if fail end err match. I don't see why they would have different messages. Also one of these has 'parseImportArgs' which I assume is leftover from a copy paste?

Are we in essence checking this

if tc.fail != (err != nil)

Alternatively, rather than storing tc.fail as a bool, store the err string to do a deeper check: possibly kind of like https://github.com/googleapis/google-cloud-go/blob/master/datastore/datastore_test.go#L1987

[markduffett]

updated to error matching pattern.