fix(install): reduce docker install timeout to 600s

1800s (30min) was too long — with systemctl mask fix, the install
should complete quickly. 600s (10min) is generous for Chinese mirrors
while not making users wait forever if something does hang.

Author: zhaojing1987

install/install_docker.sh

@@ -448,7 +448,7 @@ install_docker_custom() {
 # ---------------------------------------------------------------------------
 install_docker_official() {
   local mirrors=("" "--mirror Aliyun" "--mirror AzureChinaCloud")
-  local install_timeout=1800
+  local install_timeout=600
   local lsb_dist
   lsb_dist="$(detect_distro)"