Extract env listing code into common for reuse
Add envs command to just show environment information
Rename command from envs to env per @joelhullcio
Refactor to allow subcommands
Pull out the env code
Doh
Merge remote-tracking branch 'ContinuumIO/master' into feature/add-envs-cmd

Conflicts:
	conda/cli/main_info.py
Only pass in the relevant information

From the outside, this function only needs to know whether it should be
displaying output or not.  This allows other code to use this to create
list of environments without mocking out an args object.
Only display final \n if outputting (thanks, @asmeurer)
Merge pull request #658 from tswicegood/feature/add-envs-cmd

Extract environment list code into the common module to allow reuse