pass environment variables to tasks

Simple patch that passes the environment variables (of whatever user running dagobahd) to the task.

Note: if you run dagobahd from init/as a service, the environment variables typically aren't sourced yet.

This behavior is not replicated for remote because:

1. environment variables local to the machine/user you SSH as will be available
2. Passing environment variables from host machine is usually not useful
3. Passing environment variables, although supported by SSH config, is not implemented in paramiko because it's almost never used due to security issues.