[rust] Expose DISPLAY env in Linux and macOS

Author: bonigarcia

.bazelrc

@@ -107,6 +107,8 @@ test:windows --test_env=PATH
 test:windows --test_env=LOCALAPPDATA
 test:windows --test_env=PROGRAMFILES="C:\\Program Files"
 test:windows --test_env=PROGRAMFILES(X86)="C:\\Program Files (x86)"
+test:linux --test_env=DISPLAY
+test:macos --test_env=DISPLAY
 
 test --test_timeout=1800