Update version aliases for rpc version control

Now that Icehouse has been branched, add aliases for the rpc version
implemented by Icehouse.  These aliases can be used in the
configuration options for doing outbound rpc version control.

DocImpact - 'icehouse' is now a valid value to provide to all of the
options in the [upgrade_levels] section of nova.conf.

Closes-Bug: #1309334
Partial-Bug: #1309324
Change-Id: Iad96d8ba7e8e85346fe0b3275f220314bf76a7e3
Merge "Update version aliases for rpc version control"