test: fix unit tests to not overwrite existing cli config file (#642)

Author: ykim-akamai

Makefile

@@ -66,9 +66,12 @@ clean:
 	rm -rf dist linode_cli.egg-info build
 
 .PHONY: testunit
-testunit: export LINODE_CLI_TEST_MODE = 1
 testunit:
-	pytest -v tests/unit
+	@mkdir -p /tmp/linode/.config
+	@orig_xdg_config_home=$${XDG_CONFIG_HOME:-}; \
+	export LINODE_CLI_TEST_MODE=1 XDG_CONFIG_HOME=/tmp/linode/.config; \
+	pytest -v tests/unit; \
+	export XDG_CONFIG_HOME=$$orig_xdg_config_home
 
 .PHONY: testint
 testint: