custom: force packer install to 1.5.1

The problem with freebsd is due to packer attempting
to set ssh credentials with the temporary key before
the EC2 instance is ready.  Rather than figure out how
to get it working and risk a future release breaking
something else, let's just stick with a known working
version.

Signed-off-by: Kelley Spoon <kelley.spoon@linaro.org>
Change-Id: I97c748029d07bbac6c1f663e1a7d1dc6f52363ab
diff --git a/custom.sh b/custom.sh
index e7d727c..0927cab 100755
--- a/custom.sh
+++ b/custom.sh
@@ -51,7 +51,8 @@
 
 sed -i -e 's/#PermitTTY.*/PermitTTY yes/g' /etc/ssh/sshd_config
  
-# install packer
-wget -O- https://apt.releases.hashicorp.com/gpg | gpg --dearmor | sudo tee /usr/share/keyrings/hashicorp-archive-keyring.gpg
-echo "deb [signed-by=/usr/share/keyrings/hashicorp-archive-keyring.gpg] https://apt.releases.hashicorp.com $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/hashicorp.list
-sudo apt update && sudo apt install packer
+# install packer.  We are using an older version because current 1.8.5 has
+# a bug in it that prevents the temp ssh key from being setup for freebsd
+curl --output packer.zip https://releases.hashicorp.com/packer/1.5.1/packer_1.5.1_linux_amd64.zip  
+unzip -o packer.zip
+install -m 755 packer /usr/bin/packer