Adds help text to brocade configuration options

Help text was added to the configuration options defined in the brocade neutron
plugin. This help text should assist users of the brocade plugin. The OSTYPE
configuration option was not used in the plugin and was labeled as such so a
user of the plugin would not worry about the meaning of it.

The example etc file /etc/neutron/plugins/brocade/brocade.ini has been updated
to share the same help values where applicable.

Fixes-Bug: #1157511

Change-Id: Ie068396e77902037a7a0b5334d4dfb0dcdd3575e