Updates the Ironic on Devstack dev documentation

The current devstack configuration in the dev documentation
is out of date and will not successfully spin up a
Nova with Ironic driver environment. One of the critical
changes necessary is to set the IRONIC_VM_SPECS_RAM to 1024,
as that is now the minimum size for a virtual Ironic node.

This change also updates the configurations to more closely match
the ones being used for the virtual ironic Devstack job and
explicitly sets file logging to make debugging easier.

Change-Id: Ifbe0af9759483ccd80e74b24d45eaa4726c4b101
Merge "Updates the Ironic on Devstack dev documentation"