This defines a new local.conf file that is designed to take the place of all
of the 'pass-through'[1] configuration options that have been defined in DevStack.
* new local.conf file can contain multiple config file settings to be
merged in to existing project config files
* localrc can be embedded into local.conf and will auto-extract if
localrc does not exist
* Adds functions get_meta_section(), get_meta_section_files(),
merge_config_file() and merge_config_group()
* Adds EXTRA_OPTS, EXTRA_BAREMETAL_OPTS, Q_DHCP_EXTRA_DEFAULT_OPTS and
Q_SRV_EXTRA_DEFAULT_OPTS to the deprecated warning list at the end of stack.sh
[1] Pass-through options are those that do not configure or change DevStack's behaviour
but simply set a value in a project config file. This includes most of the EXTRA_XXX_OPTS
configuration variables.
Change-Id: I367cadc86116621e9574ac203aafdab483d810d3
893e66360c