fix(server/v2): set correct content-type for etcdError response

"net/http".Error reset the content type, so we get rid of it and
write our own one.
docs(clustering): limit for peer-address changing
fix(docs): update doc with standby info
Merge pull request #808 from robszumski/update-optimal-size

fix(docs): add information about standbys
Adding autodock into the libraries and tools section
Merge pull request #817 from cholcombe973/master

Adding autodock into the libraries and tools section
Merge pull request #816 from unihorn/95

docs(clustering): limit for peer-address changing
fix(standby_server): able to join the cluster containing itself

Standby server will switch to peer server if it finds that
it has been contained in the cluster.
tests(standby_test): comments
Merge pull request #818 from unihorn/96

fix(standby_server): able to join the cluster containing itself
tests: add TestMultiNodeKillAllAndRecorveryAndRemoveLeader

This one breaks because it doesn't set joinIndex correctly.
fix(server): set joinIndex when recovered
fix(multi_node_kill_all_and_recovery_test): ensure cluster running
fix(remove_node_test): ensure cluster config is activated
fix(simple_snapshot_test): enlarge reasonable index range
Merge pull request #814 from unihorn/91

fix(server/v2): set correct content-type for etcdError response
Merge pull request #819 from unihorn/97

fix(server): joinIndex is not set after recovery from full outage
docs(cluster-discovery): add caution to use old discovery endpoint
Merge pull request #822 from philips/add-notes-about-discovery

docs(cluster-discovery): add caution to use old discovery endpoint
fix(remove_node_test): remove unnecessary cluster configuration

The cluster configuration operation is originally to make sure
the instance won't be added back automatically between removal and
check for the number of existing peer-mode instances. But this
could make some node removed before the removal command.

Use longer sync interval instead to avoid this problem.