Parallelise format-all.sh script (#1341)

By processing each file in parallel we can make the formatting operation
faster.

Benchmarked with `time scripts/format-all.sh`:
|        	| `total` 	|
|--------	|---------	|
| Before 	| `1.892` 	|
| After  	| `0.871` 	|

Author: JackPGreen

scripts/format-all.sh

@@ -6,4 +6,9 @@
 
 find hazelcast/generated-sources hazelcast/include hazelcast/src hazelcast/test/src examples \
   | grep -E '\.(cpp|h)$'   \
-  | xargs clang-format -i
+  | while read -r file; do {
+      clang-format -i "${file}"
+    } &
+    done
+
+wait