dockerfile: add libcap-dev

Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

scripts/build/Dockerfile.tmpl

@@ -9,6 +9,7 @@ RUN apt-get update && apt-get install -y \
                 protobuf-compiler \
                 python-minimal \
                 libaio-dev \
+                libcap-dev \
                 iptables \
                 libnl-3-dev