prereqs: Add in psmisc so we can have killall

Change-Id: I1b10770f916cc77e843e283f32d313468c90ed18
diff --git a/preamble.mk b/preamble.mk
index 390b4a9..33c292c 100644
--- a/preamble.mk
+++ b/preamble.mk
@@ -69,6 +69,7 @@
 	openssh-server \
 	parted \
 	pciutils \
+	psmisc \
 	pulseaudio \
 	python \
 	python-minimal \