docker: edits to Dockerfile to install paramiko to image (#935)

Adds paramiko to the list of required packages (setup.py), and to
the popper docker image as well.

fixes #871

docs/sections/cn_workflows.md

@@ -342,6 +342,24 @@ engine-specific configuration options via the `--conf` flag.
 
 Docker is the default engine used by the `popper run`. All the 
 container configuration for the docker engine is supported by Popper.
+Popper also supports running workflows on remote docker daemons by use 
+of the `DOCKER_HOST`, `DOCKER_TLS_VERIFY` and `DOCKER_CERT_PATH` 
+variables, as explained in [the official 
+documentation][docker-remote]. For example:
+
+```bash
+export DOCKER_HOST="ssh://myuser@hostname"
+popper run -f wf.yml
+```
+
+The above runs the workflow on the `hostname` machine instead of 
+locally. It assumes the following:
+
+ 1. `myuser` has passwordless access to `hostname`, otherwise the 
+    password to the machine is requested.
+ 2. The `myuser` account can run `docker` on the remote machine.
+
+[docker-remote]: https://docs.docker.com/engine/reference/commandline/dockerd
 
 ### Singularity
 

src/Dockerfile

@@ -1,8 +1,8 @@
-FROM python:3.7.7-alpine3.12
+FROM alpine:20200917
 
 COPY . /popper
 
-RUN apk --no-cache add git && \
+RUN apk --no-cache add git py3-pip py3-paramiko && \
     pip install --no-cache-dir /popper && \
     rm -r /popper
 

src/popper/commands/cmd_help.py

@@ -13,7 +13,7 @@
 )
 @pass_context
 def cli(ctx, subcommand):
-    """ Display help for a given command or popper default help
+    """Display help for a given command or popper default help
     """
     if subcommand:
         target_command = popper_cli.get_command(ctx, subcommand)

src/setup.py

@@ -22,6 +22,7 @@
         "docker==4.3.1",
         "dockerpty==0.4.1",
         "GitPython==3.1.7",
+        "paramiko==2.7.2",
         "pykwalify==1.7.0",
         "python-box==5.1.1",
         "pyyaml==5.3.1",