The extras.d directory contains project initialization scripts to be
sourced by stack.sh at the end of its run.  This is expected to be
used by external projects that want to be configured, started and
stopped with DevStack.

Order is controlled by prefixing the script names with the a two digit
sequence number.  Script names must end with '.sh'.  This provides a
convenient way to disable scripts by simoy renaming them.

DevStack reserves the sequence numbers 00 through 09 and 90 through 99
for its own use.

The scripts are called with an argument of 'stack' by stack.sh and
with an argument of 'unstack' by unstack.sh.