dockerfile-template: install packages to support ssh-server

There is a need to recover code coverage logs from FVP containers [1] so
install required packages. Also, use docker ENV variables in the
dockerfile-template to hold packages dependencies, making it
cleaner the package installation phase.

[1] https://review.trustedfirmware.org/c/ci/tf-a-ci-scripts/+/9632

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: Iafb730c26412954026221be54d39081aa7dd2e26
diff --git a/script/docker/fvp/setup-sshd b/script/docker/fvp/setup-sshd
new file mode 100755
index 0000000..3cd9657
--- /dev/null
+++ b/script/docker/fvp/setup-sshd
@@ -0,0 +1,9 @@
+#!/bin/sh
+
+passwd -d root
+echo "PermitRootLogin yes" >> /etc/ssh/sshd_config
+echo "PermitEmptyPasswords yes" >> /etc/ssh/sshd_config
+mkdir -p /var/run/sshd
+/usr/sbin/sshd -D &
+
+exec "$@"