Dockerfile: add python-dev to fix Python.h errors

Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com>

Dockerfile

@@ -57,6 +57,7 @@ RUN apt-get update && apt-get install -y \
 	mercurial \
 	parallel \
 	pkg-config \
+	python-dev \
 	python-mock \
 	python-pip \
 	python-websocket \

Dockerfile.arm

@@ -46,6 +46,7 @@ RUN apt-get update && apt-get install -y \
 	mercurial \
 	parallel \
 	pkg-config \
+	python-dev \
 	python-mock \
 	python-pip \
 	python-websocket \

Dockerfile.gccgo

@@ -23,6 +23,7 @@ RUN apt-get update && apt-get install -y \
 	libsqlite3-dev \
 	mercurial \
 	parallel \
+	python-dev \
 	python-mock \
 	python-pip \
 	python-websocket \

Dockerfile.ppc64le

@@ -23,6 +23,7 @@ RUN apt-get update && apt-get install -y \
 	libsqlite3-dev \
 	mercurial \
 	parallel \
+	python-dev \
 	python-mock \
 	python-pip \
 	python-websocket \

Dockerfile.s390x

@@ -23,6 +23,7 @@ RUN apt-get update && apt-get install -y \
 	libsqlite3-dev \
 	mercurial \
 	parallel \
+	python-dev \
 	python-mock \
 	python-pip \
 	python-websocket \