Added main opts for test command

[imsaravana369]

Added main opts for test command, doing spago test --main modulename was failing because somehow the main option got removed in the new spago .

TODO

Checklist:

• [ ] Added the change to the "Unreleased" section of the changelog
• [ ] Added some example of the new feature to the README
• [ ] Added a test for the contribution (if applicable)

[imsaravana369]

and is creating a separate pr a overkill here? Not sure about the convention

[f-f]

Separate PR is good practice here, since every one of them is squashed in a single commit and it's good to review unrelated patches separately.