Add support for OpenStack log formats (tested on neutron, nova)

Hi,
I've been testing this format for neutron, nova log files
Can you make the timestamp regex more specific?  Something like "\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}\.\d{3}".  I ask because lnav detects the format of a file by checking every format regex it knows about against the lines of a file.  So, keeping them very specific can reduce the chance of the wrong format being used for a file.