Support task flag

[markdboyd]

Changes proposed in this pull request:

Add support for pushing apps with the --task flag. From the CLI cf push docs:

--task
Push an app that is used only to execute tasks. The app will be staged, but not started and will have no route assigned.

Things to check

• For any logging statements, is there any chance that they could be logging sensitive data?
• Are log statements using a logging library with a logging level set? Setting a logging level means that log statements "below" that level will not be written to the output. For example, if the logging level is set to INFO and debugging statements are written with log.debug or similar, then they won't be written to the otput, which can prevent unintentional leaks of sensitive data.

Security considerations

None, just adding support for new flag on cf push