Makefile: Allow $(GO) to be set with environmental variable (#2919)
Makefile: Allow $(GO) to be set with environmental variable (#2919)

* promu: Use same go invocation as prometheus' for building

If you override $(GO) var in prometheus Makefile in order to use
a custom go binary you might encounter errors while building promu
as promu's Makefile $(GO) var is also defined to look for go in the
$PATH and you might end up using different go binaries for building
prometheus and promu.

This patch makes prometheus Makefile pass its $(GO) var to promu's makefile
as environmental variable.

Signed-off-by: Sylvain Rabot <cd2ddbfaad971978dc9dc611bca495388b8445c3@lectra.com>

* Makefile: Allow $(GO) to be set with environmental variable

Signed-off-by: Sylvain Rabot <cd2ddbfaad971978dc9dc611bca495388b8445c3@lectra.com>

* Makefile: Fix hardcoded call to gofmt

Signed-off-by: Sylvain Rabot <cd2ddbfaad971978dc9dc611bca495388b8445c3@lectra.com>

GoogleCloudPlatform/prometheus,AlekSi/prometheus,amorken/prometheus,AlekSi/prometheus,prometheus/prometheus,Conorbro/prometheus,Stackdriver/stackdriver-prometheus,brancz/prometheus,Conorbro/prometheus,alileza/prometheus,brancz/prometheus,kangwoo/prometheus,amorken/prometheus,amorken/prometheus,Conorbro/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus,Gouthamve/prometheus,Gouthamve/prometheus,Gouthamve/prometheus,Conorbro/prometheus,prometheus/prometheus,Gouthamve/prometheus,Stackdriver/stackdriver-prometheus,AlekSi/prometheus,keegancsmith/prometheus,alileza/prometheus,Stackdriver/stackdriver-prometheus,prometheus/prometheus,kangwoo/prometheus,prometheus/prometheus,keegancsmith/prometheus,brancz/prometheus,keegancsmith/prometheus,Stackdriver/stackdriver-prometheus,alileza/prometheus,amorken/prometheus,brancz/prometheus,alileza/prometheus,keegancsmith/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,AlekSi/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,kangwoo/prometheus