Improving Docker based Installation (#1194)

To be able to use 'vagrant ssh' from within the docker container, it is 
necessary to run within the host network context.

Include a helper alias suggestion and a note about a current issue in 
passing arguments to vagrant options which impacts the 'vagrant ssh -c 
...' syntax with an alternative.

Dockerfile

@@ -66,6 +66,8 @@ RUN for dir in boxes data tmp; \
 
 FROM base as final
 
+ENV VAGRANT_DEFAULT_PROVIDER=libvirt
+
 COPY --from=build /vagrant /vagrant
 COPY entrypoint.sh /usr/local/bin/
 

README.md

@@ -111,6 +111,12 @@ To get the image:
 docker pull vagrantlibvirt/vagrant-libvirt:latest
 ```
 
+Preparing the docker run, only once:
+
+```bash
+mkdir -p ~/.vagrant.d/{boxes,data,tmp}
+```
+
 Running the image:
 ```bash
 docker run -it --rm \
@@ -119,10 +125,35 @@ docker run -it --rm \
   -v ~/.vagrant.d:/.vagrant.d \
   -v $(pwd):$(pwd) \
   -w $(pwd) \
+  --network host \
   vagrantlibvirt/vagrant-libvirt:latest \
     vagrant status
 ```
 
+It's possible to define an alias in `~/.bashrc`, for example:
+```bash
+alias vagrant='
+  mkdir -p ~/.vagrant.d/{boxes,data,tmp}; \
+  docker run -it --rm \
+    -e LIBVIRT_DEFAULT_URI \
+    -v /var/run/libvirt/:/var/run/libvirt/ \
+    -v ~/.vagrant.d:/.vagrant.d \
+    -v $(pwd):$(pwd) \
+    -w $(pwd) \
+    --network host \
+    vagrantlibvirt/vagrant-libvirt:latest \
+    vagrant'
+```
+
+Known issue of Docker based Installation: SSH command option cannot be used, so below command:
+```bash
+vagrant ssh master -c 'ls -la'
+```
+should be call below way:
+```bash
+vagrant ssh master -- 'ls -la'
+```
+
 Note that if you are connecting to a remote system libvirt, you may omit the
 `-v /var/run/libvirt/:/var/run/libvirt/` mount bind. Some distributions patch the local
 vagrant environment to ensure vagrant-libvirt uses `qemu:///session`, which means you