[Refactor] Move command runner to common

[at15]

currently, only part of the runner code is in util/runner, also command.go is coupled with viper, and I plan to split it out like the log package #59, so it can be used in other projects.

• move runner to common/runner, app/runner maybe better
• support direct output to file, just ignore those tty stuff like ls
• add standalone config && decouple viper
• figure out can't use rm in command runner #58 and After ctrl +c running command is not stopped #56, it happened a lot when I was using latex with Ayi and got some wrong syntax that cause latex error
• auto register command from config
  • cobra does not have command not found handler, it do return the error on https://github.com/spf13/cobra/blob/856b96dcb49d6427babe192998a35190a12c2230/command.go#L515 instead of just stop there, need to grab the code and have a look, may need to use a fork
• add functionality like foreman, allow running things in background
  • https://github.com/gdamore/govisor
  • https://github.com/mattn/goreman
  • https://github.com/ddollar/forego
  • https://github.com/DarthSim/hivemind The mind to rule processes of your development environment
  • may need a database to store more information https://github.com/boltdb/bolt
• more expressive config
  • pm2 http://pm2.keymetrics.io/docs/usage/quick-start/
  • systemd https://coreos.com/docs/launching-containers/launching/getting-started-with-systemd/
  • foreman https://github.com/ddollar/foreman it seems the foreman I used use in rails application is not https://www.theforeman.org/introduction.html which shows first in google search result
  • also consider ansible, we may use a template engine for the config, there is jinjia2 equivalent https://github.com/flosch/pongo2
• may consider using golang 1.7's new context feature
  • not to be confused with the command line's context
  • https://golang.org/pkg/context/
  • https://medium.com/@cep21/how-to-correctly-use-context-context-in-go-1-7-8f2c0fafdf39#.293ia8d47

[at15]

actually the runner is highly coupled with viper, so move it non trivial, but the util/command.go can be moved easily

[at15]

also may need sth like a context, in order to extend for things like run using shell instead of os/exec, though forcing the user to write /bin/sh -c "rm *.aux" is also an approach. context can also be used to do things like npm, where user defined tasks can be reused.

[at15]

About the register command dynamically on cobra,

cobra.OnInitialize does not work, because if you look at the code, it add the function to initializer which is executed in preRun, so it only works when certain command is invoked, help is a command, so help would show the added dummy command, but run Ayi dummy would have error.

Adding things in init will work for sure, but config files are not loaded and flags are unknown at that time

However, since cobra is executed only when RootCmd.Execute is called, dynamic adding command can be added in the wrapper. But there is still a problem, are those global flags already usable? I guess so? .... somewhere in the code, the parse for pflag should be called.

[at15]

the fallback is, for Ayi, always read these default config files and generate dynamic commands ... actually it's quite overkill

[at15]

Ansible provide a good example, http://docs.ansible.com/ansible/playbooks_intro.html

tasks:
  - name: run this command and ignore the result
    shell: /usr/bin/somecommand
    ignore_errors: True

Actually Ayi's intention is quite like Ansible