Handling ETag header for single entity GET requests and corresponding PUTs.
Some additional error handling.
Read ETags from POST/PUT responses as well.
SUMO-12582 - Merge branch 'master' of github.com:SumoLogic/sumo-java-client into chr-isearch

Conflicts:
	src/main/java/com/sumologic/client/collectors/CollectorsClient.java
	src/main/java/com/sumologic/client/search/SearchClient.java
	src/main/java/com/sumologic/client/util/HttpUtils.java