hack: fix install-tools.sh to be stand-alone utility

Commit 3cb40b8 ("hack: helper script to install auxiliary build-tools"
introduced 'install-tools.sh' script which is used by top-level Makefile
to install missing build tools. However, developer may wish to use this
script directly, and install tools under '${GOPATH}/bin' instead of
local '.bin' directory. Fixed the script to facilitate this option as
well.

Reported by Anoop C S.

Signed-off-by: Shachar Sharon <[email protected]>

Author: synarete

hack/install-tools.sh

@@ -6,7 +6,7 @@
 #
 set -e
 GO_CMD=${GO_CMD:-$(command -v go)}
-GOBIN=${GOBIN:-$(pwd)/bin}
+GOBIN=${GOBIN:-${GOPATH}/bin}
 
 _require_gobin() {
 	mkdir -p "${GOBIN}"