[DOC BLD FIX] Correct dosctring errors in disco driver
The docstring for version history at the top of the disco
driver wasn't properly formatted.  I put it in a text
code block to make it look better and to remove the
Spinx build WARNING.
@@ -108,6 +108,8 @@ CONF.register_opts(disco_opts, group=configuration.SHARED_CONF_GROUP)
class DiscoDriver(driver.VolumeDriver):
"""Execute commands related to DISCO Volumes.
+ .. code:: text
+
Version history:
1.0 - disco volume driver using SOAP
1.1 - disco volume driver using REST and only compatible
