cmd/tsuru: add FlagSet implementation to app-create

Related to #351.
cmd/tsuru: use number of units from flagset on app-create

Related to #351.
cmd/tsuru-base: simplify GuessingCommand reponsibility

It should not be responsible for checking the flag, commands should call
it only when they actually want to guess the name of the app.
cmd/tsuru-base: improve error message in GuessingCommand
cmd/tsuru-base: using --app in flagset for app-info

Related to #351.
cmd/tsuru-base: fix flag parsing in log

Related to #351.
cmd/tsuru-base: use --app in the flagset for app-grant command

Related to #351.
cmd/tsuru-base: use --app in the flagset for app-revoke command

Related to #351.
cmd/tsuru-base: use --app in the flagset for restart command

Related to #351.
cmd/tsuru-base: use --app in the flagset for run command

Related to #351.
cmd/tsuru-base: add basic implementation for Flags in GuessingCommand

I'm repeting myself :-(

Related to #351.
cmd/tsuru-base: refactoring app-info to use just GuessingCommand.Guess

Related to #351.
cmd/tsuru-base: refactoring app-grant to use just GuessingCommand.Guess

Related to #351.
cmd/tsuru-base: refactoring app-revoke to use just GuessingCommand.Guess

Related to #351.
cmd/tsuru-base: refactoring restart to use just GuessingCommand.Guess

Related to #351.
cmd/tsuru-base: remove dead code
cmd/tsuru-base: refactoring run to use just GuessingCommand.Guess

Related to #351.
cmd/tsuru-base: refactoring log to work with the new GuessingCommand

Related to #351.
cmd/tsuru-base: adapt env-get to the new GuessingCommand

Related to #351.
cmd/tsuru-base: adapt env-set to the new GuessingCommand

Related to #351.