run: Java Jar file support

Adds support for running Java Jar files directly without having to
define a Capstanfile. Capstan will automatically pull
"cloudius/osv-openjdk" base image and build new image with the Jar file
in it.

To run a Jar file, simply type:

  [penberg@nero capstan-example-java]$ capstan run target/capstan-example-java-1.0-SNAPSHOT-jar-with-dependencies.jar

and you will see something like this:

  Building capstan-example-java-1.0-SNAPSHOT-jar-with-dependencies...
  Uploading files...
  [ ... ]
  Created instance: capstan-example-java-1.0-SNAPSHOT-jar-with-dependencies
  OSv v0.13
  eth0: 192.168.122.15
  hello, world!

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>