Add Dockerfile definitions

Add alpine (musl-based) and ubuntu (glibc-based) descriptions for test
images. To run the testapp in either of them, run:

```
docker-compose run alpine
docker-compose run ubuntu
```

devtools/Dockerfile.alpine

@@ -0,0 +1,12 @@
+FROM alpine:latest
+
+RUN apk update && apk add --no-cache musl-dev libevent-dev libseccomp-dev linux-headers gcc make automake autoconf
+
+ADD . /src
+WORKDIR /src
+
+RUN ./autogen.sh
+RUN ./configure --enable-seccomp
+RUN make -j
+
+CMD make test

devtools/Dockerfile.arch

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+FROM archlinux/base:latest
+
+RUN pacman -Sy && pacman --noconfirm -S gcc automake autoconf libevent libseccomp git make perl
+RUN ln -s /usr/bin/core_perl/prove /usr/bin/prove
+
+ADD . /src
+WORKDIR /src
+
+RUN aclocal
+RUN autoheader
+RUN automake --gnu --add-missing
+RUN autoconf
+
+RUN ./configure --enable-seccomp
+RUN make -j
+
+CMD make test

devtools/Dockerfile.ubuntu

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+FROM ubuntu:latest
+
+RUN apt-get update && apt-get install -y build-essential automake1.11 autoconf libevent-dev libseccomp-dev git
+
+ADD . /src
+WORKDIR /src
+
+RUN ./autogen.sh
+RUN ./configure --enable-seccomp
+RUN make -j
+
+CMD make test

docker-compose.yml

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+version: '3'
+services:
+    alpine:
+        build:
+            context: .
+            dockerfile: devtools/Dockerfile.alpine
+    ubuntu:
+        build:
+            context: .
+            dockerfile: devtools/Dockerfile.ubuntu
+    arch:
+        build:
+            context: .
+            dockerfile: devtools/Dockerfile.arch