move the backup file to acme home

fix https://github.com/Neilpang/acme.sh/issues/488

acme.sh

@@ -2059,6 +2059,10 @@ _initpath() {
     _debug DOMAIN_PATH "$DOMAIN_PATH"
   fi
 
+  if [ -z "$DOMAIN_BACKUP_PATH" ]; then
+    DOMAIN_BACKUP_PATH="$DOMAIN_PATH"
+  fi
+
   if [ -z "$DOMAIN_CONF" ]; then
     DOMAIN_CONF="$DOMAIN_PATH/$domain.conf"
   fi
@@ -3612,7 +3616,7 @@ _installcert() {
 
     _info "Installing cert to:$Le_RealCertPath"
     if [ -f "$Le_RealCertPath" ] && [ ! "$IS_RENEW" ]; then
-      cp "$Le_RealCertPath" "$Le_RealCertPath".bak
+      cp "$Le_RealCertPath" "$DOMAIN_BACKUP_PATH/cert.bak"
     fi
     cat "$CERT_PATH" >"$Le_RealCertPath"
   fi
@@ -3625,7 +3629,7 @@ _installcert() {
       cat "$CA_CERT_PATH" >>"$Le_RealCACertPath"
     else
       if [ -f "$Le_RealCACertPath" ] && [ ! "$IS_RENEW" ]; then
-        cp "$Le_RealCACertPath" "$Le_RealCACertPath".bak
+        cp "$Le_RealCACertPath" "$DOMAIN_BACKUP_PATH/ca.bak"
       fi
       cat "$CA_CERT_PATH" >"$Le_RealCACertPath"
     fi
@@ -3635,7 +3639,7 @@ _installcert() {
 
     _info "Installing key to:$Le_RealKeyPath"
     if [ -f "$Le_RealKeyPath" ] && [ ! "$IS_RENEW" ]; then
-      cp "$Le_RealKeyPath" "$Le_RealKeyPath".bak
+      cp "$Le_RealKeyPath" "$DOMAIN_BACKUP_PATH/key.bak"
     fi
     cat "$CERT_KEY_PATH" >"$Le_RealKeyPath"
   fi
@@ -3644,7 +3648,7 @@ _installcert() {
 
     _info "Installing full chain to:$Le_RealFullChainPath"
     if [ -f "$Le_RealFullChainPath" ] && [ ! "$IS_RENEW" ]; then
-      cp "$Le_RealFullChainPath" "$Le_RealFullChainPath".bak
+      cp "$Le_RealFullChainPath" "$DOMAIN_BACKUP_PATH/fullchain.bak"
     fi
     cat "$CERT_FULLCHAIN_PATH" >"$Le_RealFullChainPath"
   fi