Replace USER with BUILD_USERNAME

USER may be "nobody" if the build is sandboxed. BUILD_USERNAME will have
the original value in all cases.

Bug: 122270019
Test: none
Change-Id: Ic64f842864a9e79ea2179228370bb4fd92541d20
diff --git a/version.mk b/version.mk
index 375249e..90fe55e 100644
--- a/version.mk
+++ b/version.mk
@@ -97,7 +97,7 @@
 ifeq ($(strip $(HAS_BUILD_NUMBER)),false)
     git_hash := $(shell git --git-dir $(LOCAL_PATH)/.git log -n 1 --pretty=format:%h)
     date_string := $(shell date +%Y-%m-%d)
-    version_name_package := $(base_version_major).$(base_version_minor).$(code_version_build) (eng.$(USER).$(git_hash).$(date_string)-$(base_version_arch)$(base_version_density))
+    version_name_package := $(base_version_major).$(base_version_minor).$(code_version_build) (eng.$(BUILD_USERNAME).$(git_hash).$(date_string)-$(base_version_arch)$(base_version_density))
 else
     version_name_package := $(base_version_major).$(base_version_minor).$(code_version_build) ($(BUILD_NUMBER_FROM_FILE)-$(base_version_arch)$(base_version_density))
 endif