This struct is responsible for determining the name and
root dir of the executable.

The `RootDir` property will be used to find the config.

The `Name` property will be used to determine what `Command`
and `CommandArgs` to be built.

Other functions are still expecting for `CommandArgs` instead
of `Shell`. They should be expecting `commandargs.Shell` now
since it has been renamed.

`CommandArgs` has been renamed to `Shell`.

An interface has been added that includes `Executable()` and
`Arguments()` method. The `BaseArgs` implement this methods
and should be embeeded in each type.

Rename the ruby scripts to have `-ruby` suffix and add a symlink
for both to `./gitlab-shell`. The executable name will be used to
determine how args will be parsed.

For now, we only parse the arguments for gitlab-shell commands. If
the executable is `gitlab-shell-authorized-keys-check` or
`gitlab-shell-authorized-principals-check`, it'll always fallback
to the ruby version.

Ruby specs test the ruby script, the fallback from go to ruby and
go implementation of both (still pending).

Update rubygems version on CI for go tests

See merge request gitlab-org/gitlab-shell!320

Resolve "Update .PHONY to have accurate list of targets"

Closes #198

See merge request gitlab-org/gitlab-shell!316