Support command/exec lists

[eikenb]

Currently configured commands/execs can take 2 forms. A single word/command (no spaces) that will get run directly on any supported OS and a full shell command line (with spaces) that is supported on *nix systems with an standard shell (/bin/sh) available. This limits the ability of people who do not have the shell available to only running single word commands which might be tough in some setups (might require a small binary wrapper).

To better support multiple command execution environments add support for direct execution lists. That is the command in a list form, with the list elements separated on the spaces of the command. These will be parsed into a Go string slice which can be directly passed to the underlying OS execution system call. This would then allow all commands, even those with arguments, to be directly run without the need for the wrapping shell call.

Some examples of what this will probably look like...

In HCL:

command = ["/usr/local/bin/awesome-app", "server"]

In JSON:

"command": ["/usr/local/bin/awesome-app", "server"]