The current mechanism to get the tag name doesn't work well.

When a new commit lands to the master branch, the master branch is
not named correctly

i.e:
```
rsevilla@wonderland /tmp/foo (master) $ git describe --tags 2>/dev/null || git rev-parse --abbrev-ref HEAD | sed 's/master/latest/g'
v1.0.0-1-g487fada
rsevilla@wonderland /tmp/foo (master) $ git log --oneline | head
487fada Foo
12701a6 Added exit status for uperf failures (#782)
94005cd missing env var num_pairs (#784)
```

Signed-off-by: Raul Sevilla <[email protected]>

Makefile

@@ -41,8 +41,8 @@ ARCH ?= $(shell uname -m | sed 's/x86_64/amd64/')
 REGISTRY ?= quay.io
 ORG ?= cloud-bulldozer
 # Get the current branch name
-# In case this is the master branch, rename it to latest
-VERSION ?= $(shell git describe --tags 2>/dev/null || git rev-parse --abbrev-ref HEAD | sed 's/master/latest/g')
+# In case is the master branch, rename it to latest
+VERSION ?= $(shell hack/tag_name.sh)
 IMG ?= $(REGISTRY)/$(ORG)/benchmark-operator:$(VERSION)
 ifdef IMAGE_ARCH
 IMG := $(REGISTRY)/$(ORG)/benchmark-operator:$(VERSION)-$(IMAGE_ARCH)

hack/tag_name.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+if [[ -z $(git branch --show-current) ]]; then
+  git describe --tags --abbrev=0
+else
+  git branch --show-current | sed 's/master/latest/g'
+fi