This commit adds the necessary changes to support users with multiple
`GOPATH` workspaces. Previously the `getSrcPath()` function in
`cobra/cmd/helpers.go` would not take into account the fact the the
system `GOPATH` returns a colon-separated list if system was configured
with multiple GOPATH workspaces. If the GOPATH was set to be
`/foo/a:/bar/b`, it would simply append `src/` to the end of the string
literal giving `/foo/a:/bar/b/src` which resulted in undesired behavior.
Following the specs the changeset here adds support for multiple GOPATH
workspaces and if a given package directory is not to be found in any of
the workspaces the first one is chosen, i.e. for `cobra init` it will
first check all workspaces for the specified project and settling on the
first (`/foo/a`) if nothing found.
This preserves backwards compatibility as single workspace environments
are provably unaffected by these changes.
