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/tests/functions.sh b/tests/functions.sh
index 06a4134..874d022 100755
--- a/tests/functions.sh
+++ b/tests/functions.sh
@@ -42,7 +42,7 @@
 
 echo "Testing enable_service()"
 
-function test_enable_service() {
+function test_enable_service {
     local start="$1"
     local add="$2"
     local finish="$3"
@@ -68,7 +68,7 @@
 test_enable_service 'a,b,-c' c 'a,b'
 test_enable_service 'a,b,c' -c 'a,b'
 
-function test_disable_service() {
+function test_disable_service {
     local start="$1"
     local del="$2"
     local finish="$3"
@@ -109,7 +109,7 @@
 echo "Testing disable_negated_services()"
 
 
-function test_disable_negated_services() {
+function test_disable_negated_services {
     local start="$1"
     local finish="$2"