build.make: allow repos to use 'go mod' for vendoring

[pohly]

How a repo does vendoring is detected based on the presence of
Gopkg.toml.

The vendor check with dep was all done locally, but the
corresponding check for go mod requires network access. The check
therefore gets skipped when running in the Prow CI in situations where
we are sure that it isn't needed (for example, in a periodic job).

This is required for kubernetes-csi/csi-test#188

allow vendoring with 'go mod'

/kind feature

[k8s-ci-robot]

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[pohly]

/assign @bswartz

[hoyho]

may get an error when execute git status --porcelain=2 -- vendor | wc -l with different git version?

 [root@vm43 csi-test]# git status --porcelain=2 -- vendor | wc -l
error: option `porcelain' takes no value
usage: git status [options] [--] <pathspec>...

    -v, --verbose         be verbose
    -s, --short           show status concisely
    -b, --branch          show branch information
    --porcelain           machine-readable output
    --long                show status in long format (default)
    -z, --null            terminate entries with NUL
    -u, --untracked-files[=<mode>]
                          show untracked files, optional modes: all, normal, no. (Default: all)
    --ignored             show ignored files
    --ignore-submodules[=<when>]
                          ignore changes to submodules, optional when: all, dirty, untracked. (Default: all)
    --column[=<style>]    list untracked files in columns

0

[pohly]

Which version of git are you using?

We can drop the =2, the original format should be good enough. All we care for is "empty" vs. "not empty" anyway.

[pohly]

Thanks for testing, BTW.

[pohly]

I've removed the =2.

[msau42]

/lgtm