add capability to bootstrap from DNS
Add a simple test and mock for genDNS
fix from comments
add apurl checking and logging
Fully resolve DNS entries to IPs and ignore single errors (such as no etcd-server-ssl)
rename flag to discovery-srv
resolve all hostnames in DNS discovery
docs: add dns bootstrap guide
change logging
Merge pull request #1947 from barakmich/dns_bootstrap

add capability to bootstrap from DNS SRV
Merge pull request #1973 from kelseyhightower/dns-bootstrap-docs

docs: add dns bootstrap guide
docs: document DNS bootstrapping
Merge pull request #1977 from kelseyhightower/update-clustering-docs

docs: document DNS bootstrapping
etcdmain: add config.go
Merge pull request #1976 from xiang90/flag

etcdmain: add config.go
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  etcdmain: add config.go
  docs: document DNS bootstrapping
  change logging
  docs: add dns bootstrap guide
  resolve all hostnames in DNS discovery
  rename flag to discovery-srv
  Fully resolve DNS entries to IPs and ignore single errors (such as no etcd-server-ssl)
  add apurl checking and logging
  fix from comments
  Add a simple test and mock for genDNS
  add capability to bootstrap from DNS