Improve CLI command parsing

[pires]

• CHANGELOG.md updated
• Rebased/mergeable
• Tests pass
• Sign CLA (if not already signed)

Now, the output:

$ influx -host 192.168.99.100
Visit https://enterprise.influxdata.com to register for updates, InfluxDB server management, and monitoring.
Connected to http://192.168.99.100:8086 version 0.9.3
InfluxDB shell 0.9
> user
ERR: error parsing query: found USER, expected SELECT, DELETE, SHOW, CREATE, DROP, GRANT, REVOKE, ALTER, SET at line 1, char 1
Warning: It is possible this error is due to not setting a database.
Please set a database with the command "use <database>".
> use
Could not parse database name from "use".

Refs #4588
Fixes #4544

[pires]

While this fixes the issue it can be further improved.

>     use metrics
Using database metrics
> use  metrics
Could not parse database name from "use  metrics".

While I understand one may argue this tool is not meant to be dumb-proof, I like to make it harder to commit mistakes while using it. I'll probably be looking at fixing the above.

[corylanou]

This makes sense. Can you add some tests that show what was fixed?

[pires]

Sure.

[pires]

@corylanou care to review?

[corylanou]

nit: looks like we picked up an extra line here.

[pires]

Fixed.

[corylanou]

One nit, otherwise +1. Thanks again!

[pires]

@corylanou nit fixed. Thank you.

[otoolep]

This needs rebasing now.

[otoolep]

Makes sense, +1.

[otoolep]

Let us know when you rebase @pires and I will then merge.

[pires]

@otoolep ready.

[otoolep]

Thanks again @pires