snapcraft: Add vendoring support
snapcraft: Add vendoring support

Also, build with go1.8, run "make test", and strip the binary.

Fixes #3226

fedelibre/hugo,mitchchn/hugo,gohugoio/hugo,mdhender/hugo,anthonyfok/hugo,fedelibre/hugo,gohugoio/hugo,digitalcraftsman/hugo,fedelibre/hugo,anthonyfok/hugo,mdhender/hugo,mdhender/hugo,fedelibre/hugo,anthonyfok/hugo,gohugoio/hugo,mitchchn/hugo,mdhender/hugo,digitalcraftsman/hugo