Remove the right socket before starting the daemon

For some reason, an old socket occasionally stays here on OSX, causing
the subsequent tests to fail

(cherry picked from commit c2c0dba792)

tests/common.sh.in

@@ -86,10 +86,10 @@ startDaemon() {
     fi
     # Start the daemon, wait for the socket to appear.  !!!
     # ‘nix-daemon’ should have an option to fork into the background.
-    rm -f $NIX_STATE_DIR/daemon-socket/socket
+    rm -f $NIX_DAEMON_SOCKET_PATH
     ${NIX_DAEMON_COMMAND:-nix-daemon} &
     for ((i = 0; i < 30; i++)); do
-        if [ -e $NIX_DAEMON_SOCKET_PATH ]; then break; fi
+        if [[ -S $NIX_DAEMON_SOCKET_PATH ]]; then break; fi
         sleep 1
     done
     pidDaemon=$!