blesse-builds: Build the tag we're seeing

Instead of trying to guess the right tag just use what
jenkins gives us right away.

blessed_build_auto.groovy

@@ -83,19 +83,17 @@ pkgs.each { pkg ->
           fi
           """
 
-        scm_tag_cmd = """commit="\$(git for-each-ref --sort=taggerdate --format '%(objectname)' refs/tags | tail -n 1)"; head_tag="\$(git describe --exact-match --tags \${commit})" 2> /dev/null || exit 128""".stripIndent()
         scm_verify_tag_cmd = """git tag -v "\${head_tag}" || exit 64""".stripIndent()
 
         scm_checkout_cmd = """cd build
             ${submodule_update_cmd}
             git clean -dfx
-            $scm_tag_cmd
-            git checkout -f "\${head_tag}"
         """.stripIndent()
 
         build_cmd = """
             rm -f *.deb *.changes *.dsc *.upload *.tar.* *.buildinfo *.build
             ${scm_checkout_cmd}
+            head_tag=\$(git describe HEAD)
             ${scm_verify_tag_cmd}
 
             # changelog distribution needs to be byzantium or landing