test framework: Unset no_proxy as well

This caused test-bug-717891-abolute-uris-for-proxies to fail

Gbp-Dch: ignore

test/integration/framework

@@ -398,7 +398,7 @@ EOF
 	export LC_ALL=C.UTF-8
 	unset LANGUAGE APT_CONFIG
 	unset GREP_OPTIONS DEB_BUILD_PROFILES
-	unset http_proxy HTTP_PROXY https_proxy HTTPS_PROXY
+	unset http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy
 	msgdone "info"
 }