fix(server/v1): don't fail put on new v1 key

We weren't checking for PrevNode being nil in the v1 code path. Do this
and add a test.

Fixes #557
Merge pull request #558 from philips/v1-put-crash-fix

fix(server/v1): don't fail put on new v1 key
fix(Documentation): single machine clusters have some stats undefined

document that single machine clusters will omit sendBandwidthRate and
sendPkgRate.

Via http://thread.gmane.org/gmane.comp.distributed.etcd/218
add(server/v1/tests): Port many of the v2 HTTP handler tests to v1

This should cover most aspects of the v1 API but being new to the etcd
code base I cannot promise that or that the tests are even correct.
They do pass though :)
Merge pull request #560 from marineam/test-v1

add(server/v1/tests): Port many of the v2 HTTP handler tests to v1
fix(server/tls_info): use all certificates in CA file

fixes coreos/etcd#553
Merge pull request #554 from mfischer-zd/tls_fixes

fix(server/tls_info): use all certificates in CA file
Merge pull request #559 from philips/document-missing-stats

fix(Documentation): single machine clusters have some stats undefined