Adding ISO tools in builder container

We need to be able to work with ISO images inside builder container.
This change makes the stx-builder privileged so we can mount a
filesystem inside it and we add mkisofs, isomd5sum and syslinux-utils
packages to be installed when building the image.

Test plan:
    PASS: Build stx-builder image.
    PASS: Run ./stx-init-env --rebuild with success.

Story: 2010676
Task: 50189

Change-Id: I44b0d99965befd9e78934ff3dbcbe4bdf02514af
Signed-off-by: Dostoievski Batista <dostoievski.albinobatista@windriver.com>

stx/dockerfiles/stx-builder.Dockerfile

@@ -56,6 +56,9 @@ RUN apt-get update && apt-get install --no-install-recommends -y \
         vim \
         wget \
         xz-utils \
+        mkisofs \
+        isomd5sum \
+        syslinux-utils \
         && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/*

stx/stx-build-tools-chart/stx-builder/values.yaml

@@ -58,7 +58,8 @@ dnsConfig:
 podSecurityContext: {}
 # fsGroup: 2000
 
-securityContext: {}
+securityContext:
+  privileged: true
 # capabilities:
 #   drop:
 #   - ALL