Add docker testing for Gentoo

Signed-off-by: Alexey Neyman <stilor@att.net>

testing/docker/common-scripts/su-as-user

@@ -8,6 +8,7 @@ shift 4
 
 groupadd -g ${gid} ${grp}
 useradd -d /home/${usr} -m -g ${gid} -u ${uid} ${usr}
+rm -f /home/${usr}/src
 ln -sf /src /home/${usr}/src
 if [ -z "$*" ]; then
     exec su -l ${usr}

testing/docker/dmgr.sh

@@ -83,7 +83,10 @@ action_clean()
     local cntr=$1
 
     msg "Cleaning up after ${cntr}"
-    rm -rf build-${cntr}
+    if [ -d build-${cntr} ]; then
+        chmod -R +w build-${cntr}
+        rm -rf build-${cntr}
+    fi
 }
 
 action=$1

testing/docker/gentoo-amd64/Dockerfile

@@ -0,0 +1,4 @@
+FROM gentoo/stage3-amd64-hardened
+RUN wget -O /sbin/dumb-init https://github.com/Yelp/dumb-init/releases/download/v1.2.1/dumb-init_1.2.1_amd64
+RUN chmod +x /sbin/dumb-init
+ENTRYPOINT [ "/sbin/dumb-init", "--" ]