Enforce function declaration format in bash8

Check that function calls look like ^function foo {$ in bash8, and fix
all existing failures of that check.  Add a note to HACKING.rst

Change-Id: Ic19eecb39e0b20273d1bcd551a42fe400d54e938
diff --git a/lib/cinder_plugins/glusterfs b/lib/cinder_plugins/glusterfs
index a0c5ae8..b4196e4 100644
--- a/lib/cinder_plugins/glusterfs
+++ b/lib/cinder_plugins/glusterfs
@@ -27,7 +27,7 @@
 # ------------
 
 # configure_cinder_driver - Set config files, create data dirs, etc
-function configure_cinder_driver() {
+function configure_cinder_driver {
     # To use glusterfs, set the following in localrc:
     # CINDER_DRIVER=glusterfs
     # CINDER_GLUSTERFS_SHARES="127.0.0.1:/vol1;127.0.0.1:/vol2"