GNS3 ipterm image with support for dhclient instead of udhcpc

Dockerfile

FROM gns3/ipterm:latest

RUN DEBIAN_FRONTEND=noninteractive && \
        apt-get -q update && \
        apt-get -qq -y install isc-dhcp-client && \
        rm -rf /var/lib/apt/lists/*

# Need to make dhclient available during init script execution
# RUN mkdir -p /tmp/gns3/bin && ln -s /sbin/dhclient /tmp/gns3/bin/dhclient
# ^^ does not work as directory /tmp/gns/bin should not exist.
#
# Solution is to use the pre-up script in the interfaces file to
# create the symlink.