etcdserver: have newMember take an optional time field

This will be used by members joining an existing cluster or joining
using discovery.
etcdserver: stop using addScheme

This standardizes the flags to use a list of URLs everywhere. The next
step is to enforce the scheme based on TLS settings and support compat
flags.
Merge pull request #1213 from philips/improve-cluster

etcdserver: stop using addScheme
etcdserver: stop worrying about scheme

Stop worrying about the scheme. This puts a TODO on adding validation to
the schemes if TLS is specified. But we can worry about that later.
Merge pull request #1216 from philips/improve-cluster-procfile

etcdserver: stop worrying about scheme
main: not use loop variable in goroutine in loop body

Because loop variable are reused in following loops.
flags/urls: assign urls instead of append
Merge pull request #1217 from unihorn/146

main: not use loop variable in goroutine in loop body
Merge pull request #1218 from unihorn/147

flags/urls: assign urls instead of append
etcdserver: apply config change on cluster store