Install clang-tools-6.0 package

The clang-tools contains 'scan-build' binary, used for static analysis
checks at TF-A project [1].

[1] https://git.trustedfirmware.org/ci/tf-a-ci-scripts.git/tree/script/scan_build_wrapper.sh

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: I909b264f880821f61a1e49bafb11737f77c863f5
diff --git a/bionic-amd64-tf-m-build/Dockerfile b/bionic-amd64-tf-m-build/Dockerfile
index 7376014..66bcd9d 100644
--- a/bionic-amd64-tf-m-build/Dockerfile
+++ b/bionic-amd64-tf-m-build/Dockerfile
@@ -9,6 +9,7 @@
 ENV PKG_DEPS="\
     bison \
     build-essential \
+    clang-tools-6.0 \
     curl \
     default-jre \
     device-tree-compiler \