build: add an env var to run make reset unattended (#13820)

- previously "make reset" was expecting user input from the terminal
    to do its job
  - setting UNATTENDED to any non-zero string will allow "make reset" to
    run without interactive confirmation

Signed-off-by: Mathieu Launay <m.launay@criteo.com>

Makefile.work

@@ -44,6 +44,16 @@
 #  * ENABLE_AUTO_TECH_SUPPORT: Enable the configuration for event-driven techsupport & coredump mgmt feature
 #  *                 Default: y
 #  *                 Values: y,n
+#  * INCLUDE_BOOTCHART: Install SONiC bootchart
+#  *                 Default: y
+#  *                 Values: y,n
+#  * ENABLE_BOOTCHART: Enable SONiC bootchart
+#  *                 Default: n
+#  *                 Values: y,n
+#  * UNATTENDED: Don't wait for interactive input from terminal, setting this
+#  *             value to anything will enable it
+#  *             Default: unset
+#  *             Value: y
 #
 ###############################################################################
 
@@ -482,8 +492,13 @@ init :
 
 .ONESHELL : reset
 reset :
-	@echo && echo -n "Warning! All local changes will be lost. Proceed? [y/N]: "
-	@read ans && (
+	@echo && (
+	if [ -z "$(UNATTENDED)" ]; then
+	    echo -n "Warning! All local changes will be lost. Proceed? [y/N]: "
+	    @read ans
+	else
+	    ans=y
+	fi
 	if [ $$ans == y ]; then
 	    echo "Resetting local repository. Please wait...";
 	    sudo rm -rf fsroot*;