nix: added custom build to allow turning off the sandbox

Makefile

@@ -1,5 +1,5 b''
 
-.PHONY: clean docs docs-clean docs-cleanup test test-clean test-only test-only-postgres test-only-mysql web-build generate-pkgs pip-packages
+.PHONY: clean docs docs-clean docs-cleanup test test-clean test-only test-only-postgres test-only-mysql web-build generate-pkgs pip-packages build-nix
 
 NODE_PATH=./node_modules
 WEBPACK=./node_binaries/webpack
@@ -66,4 +66,7 b' generate-js-pkgs:'
 
 generate-license-meta:
 	nix-build pkgs/license-generate.nix -o result-license && \
-	cat result-license/licenses.json | python -m json.tool > rhodecode/config/licenses.json
  No newline at end of file
+	cat result-license/licenses.json | python -m json.tool > rhodecode/config/licenses.json
+
+build-nix:
+	nix-build --show-trace --option sandbox false --option max-jobs 4 --option cores 4