Check server status before changing it

Fixes grnet/kamaki#57

This fix affects the CLI commands "server_start", "server_reboot"
and "server_shutdown" which are specified in "kamaki.cli.cmds.cyclades".
These are the operations that modify the status of a server.

The problem was caused when the target status was the same as the current.
In this case, the request for status modification would fail with a 400
error code response. At this point, kamaki couldn't have adequate information
to correctly evaluate the error.

This problem is solved by checking the current status before attempting to
modify it.  Also, the server ID is validated in advance, instead of waiting
for a 400 server error.
Update general information and setup instructions

Refs grnet/kamaki#49
Write a set of short scripts using the kamaki lib

Fixes grnet/kamaki#49
Return volume metadata in "create_volume"

The method used to return results in this format:
  {"volume": {"id": ..., "display_name" ..., ...}}
It now returns the results in this form:
  {"id" ..., "display_name" ..., ...}
as it is the case with every other creation command in kamaki library.
Support old history files

Fixes grnet/kamaki#80

Kamaki history files must have an offset counter on the first line,
since version 0.11.

With this fix, kamaki supports older history files and adds the
default offset counter at the first line.
Fix pithos client tests and pep8 errors