[#439] Add --vars-inline that is capable of overwriting --vars

[pedroMMM]

Checklist

• make test-all (UNIX) passes. CI will also test this
• unit and/or integration tests are included (if applicable)
• documentation is changed or added (if applicable)

Description of change

Add --vars-inline to dynamically pass variables which can overwrite variables sourced from --vars, but with no deep merging.

Closes #439

[aelsabbahy]

I'll review this over the weekend. At first glance tests/results it looks great.

[aelsabbahy]

So, trying this out, and seems like there's either a bug in the code, or I'm misunderstanding it.
goss.yaml

package:
  coreutils:
    installed: true

$ goss --vars-inline '{"package": "coreutils"}' render
panic: assignment to entry in nil map

goroutine 1 [running]:
github.com/aelsabbahy/goss.NewTemplateFilter(0x0, 0x0, 0x7ffc125b2ee8, 0x18, 0x18)
        /home/aelsabbahy/sandbox/golang/src/github.com/aelsabbahy/goss/template.go:68 +0x1cf
github.com/aelsabbahy/goss.RenderJSON(0xc0000d4dc0, 0xc0000b272f, 0x9de627)
        /home/aelsabbahy/sandbox/golang/src/github.com/aelsabbahy/goss/store.go:137 +0x162
main.main.func3(0xc0000d4dc0, 0xc0000b6800, 0xc0000d4d00)
        /home/aelsabbahy/sandbox/golang/src/github.com/aelsabbahy/goss/cmd/goss/goss.go:153 +0x2f
github.com/urfave/cli.HandleAction(0x92ba60, 0xa02330, 0xc0000d4dc0, 0xc0000b6800, 0x0)
        /home/aelsabbahy/sandbox/golang/pkg/mod/github.com/urfave/cli@v0.0.0-20161102131801-d86a009f5e13/app.go:471 +0xad
github.com/urfave/cli.Command.Run(0x9ded3b, 0x6, 0x0, 0x0, 0xc000093f50, 0x1, 0x1, 0x9ea921, 0x1d, 0x0, ...)
        /home/aelsabbahy/sandbox/golang/pkg/mod/github.com/urfave/cli@v0.0.0-20161102131801-d86a009f5e13/command.go:191 +0x924
github.com/urfave/cli.(*App).Run(0xc0000a1860, 0xc0000b8040, 0x4, 0x4, 0x0, 0x0)
        /home/aelsabbahy/sandbox/golang/pkg/mod/github.com/urfave/cli@v0.0.0-20161102131801-d86a009f5e13/app.go:241 +0x654
main.main()
        /home/aelsabbahy/sandbox/golang/src/github.com/aelsabbahy/goss/cmd/goss/goss.go:343 +0x1e68

I tried:

--vars-inline '{"package": "coreutils"}'
--vars-inline '{package: coreutils}'
--vars-inline 'package: coreutils'

[aelsabbahy]

Oh, found the bug! seems --vars-inline doesn't work if --vars isn't provided

[pedroMMM]

Great catch! Thank you, I will address this bug as soon I have some time. I have been very busy with repairs at the new house...

[aelsabbahy]

Congrats on the new house. :)

[pedroMMM]

Thank you @aelsabbahy for the patience, it's ready to be reviewed again. I finally had some uninterrupted free time to wrap my head around Goss.

I abstracted the calls to load the variables and merge them and unit test it to ensure no other problems from now on.

I got problems on Code Climate so I tweaked the TemplateFilter in the template.go to satisfy Code Climate and simplify efforts like the one raised recently on #544.

[aelsabbahy]

Looks great, small change to env var naming and then it's ready to go.

Thanks for the great contributions!