Block host power on when ActivationBlocksTransition exists

Add a dependency to the power on target so that it waits to
start until the ActivationBlocksTransition interface is not
present on any of the Software subtrees, which would indicate
that a code update is in progress.

Closes openbmc/openbmc#1344

Change-Id: I926d209ce4d3106e09e35a35c1e9cfde1ec2f613
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/common/recipes-phosphor/dbus/phosphor-mapper/mapper-subtree-remove@.service b/common/recipes-phosphor/dbus/phosphor-mapper/mapper-subtree-remove@.service
new file mode 100644
index 0000000..75dd9ab
--- /dev/null
+++ b/common/recipes-phosphor/dbus/phosphor-mapper/mapper-subtree-remove@.service
@@ -0,0 +1,10 @@
+[Unit]
+Description=mapper subtree-remove %I
+Wants=obmc-mapper.target
+After=obmc-mapper.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=no
+Restart=no
+ExecStart={sbindir}/mapper subtree-remove %I