Move shared devstack functions to functions-common

Syncing devstack/functions-common -> grenade/functions is confusing,
and as a result grenade/functions has been updated with grenade-specific
stuff.  This moves existing functions to 'functions-common' and isolates
grenade specific things to 'functions'.  'functions' sources 'functions-common'
so this should not require any other changes and will make it easier to keep
code synced with devstack.

Change-Id: I3b6324fc3067833075fc5487684d31593627b779
Merge "Move shared devstack functions to functions-common"