cmd/viewcore/vendor: vendor third-party pkgs for viewcore

Viewcore uses github.com/spf13/cobra for command line interface.
We vendor the package and other required packages for reproducible
build and testing.

  github.com/spf13/cobra
  github.com/spf13/pflag
  github.com/inconshreveable/mousetrap

Change-Id: I424b89c50900b5e89bf38aa8b0c82d64ba62cbc9
Reviewed-on: https://go-review.googlesource.com/115056
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
70 files changed