iotests: Drop use of bash keyword 'function'

Bash allows functions to be declared with or without the leading
keyword 'function'; but including the keyword does not comply with
POSIX syntax, and is confusing to ksh users where the use of the
keyword changes the scoping rules for functions.  Stick to the
POSIX form through iotests.

Done mechanically with:
  sed -i 's/^function //' $(git ls-files tests/qemu-iotests)

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20181116215002.2124581-1-eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

tests/qemu-iotests/049

@@ -40,13 +40,13 @@ _supported_fmt qcow2
 _supported_proto file
 _supported_os Linux
 
-function filter_test_dir()
+filter_test_dir()
 {
     sed -e "s#$IMGPROTO:$TEST_DIR#TEST_DIR#g" \
         -e "s#$TEST_DIR#TEST_DIR#g"
 }
 
-function test_qemu_img()
+test_qemu_img()
 {
     echo qemu-img "$@" | filter_test_dir
     $QEMU_IMG "$@" 2>&1 | filter_test_dir