Add dependency management (version) for 'org.awaitility:awaitility'.

Set Awaitility to version 4.0.3 at present.

gradle.properties

@@ -1,6 +1,7 @@
 org.gradle.jvmargs=-Xmx2g -Dfile.encoding=UTF-8
 antlrVersion=2.7.7
 apacheGeodeVersion=1.13.0
+awaitilityVersion=4.0.3
 byteBuddyVersion=1.10.18
 findbugsVersion=3.0.2
 mockitoVersion=3.6.0