Slaves file is now a template.

Change 0dc868e removed the `conf/slaves` file and made it a template like most of the other configuration files. This means you can no longer run `make-distribution.sh` unless you manually create a slaves file to be statically bundled in your distribution, which seems at odds with making it a template file.

Author: Sarah Gerweck <sarah.a180@gmail.com>

Closes #2549 from sarahgerweck/noMoreSlaves and squashes the following commits:

d11d99a [Sarah Gerweck] Slaves file is now a template.
[Build]remove spark-staging-1030

Since 1.1.0 has published, remove spark-staging-1030.

Author: wangfei <wangfei1@huawei.com>

Closes #2532 from scwf/patch-2 and squashes the following commits:

bc9e00b [wangfei] remove spark-staging-1030
[SQL][DOCS] Clarify that the server is for JDBC and ODBC

Author: Michael Armbrust <michael@databricks.com>

Closes #2527 from marmbrus/patch-1 and squashes the following commits:

a0f9f1c [Michael Armbrust] [SQL][DOCS] Clarify that the server is for JDBC and ODBC