Sync the doc with latest code

Our agent_ipmitool, agent_ilo, iscsi_ilo, pxe_ilo and agent_pyghmi
drivers also support sending notifications to Ceilometer. However,
in our install-guide.rst, we just mentioned pxe_ipmitool and
pxe_ipminative drivers, so the documentation needs to be synced with
current code.

Change-Id: Ic6dec44ba11177d0a350c5b4e3cf1eae3658c1b7
Closes-Bug: #1369838
Merge "Sync the doc with latest code"