Add exists() and waitForX() to cdap-client classes
Addressed comments
Merge branch 'develop' of github.com:caskdata/cdap into feature/improve-client

Conflicts:
	cdap-client/src/main/java/co/cask/cdap/client/DatasetClient.java
	cdap-client/src/main/java/co/cask/cdap/client/DatasetModuleClient.java
	cdap-client/src/main/java/co/cask/cdap/client/DatasetTypeClient.java
Fixed sleepDelay bug in ProgramFlowUtil
Merge pull request #557 from caskdata/feature/improve-client

CDAP-398 Add exists() and waitForX() to cdap-client classes