Added validation checks to HDP plugin

Included checks for namenode, jobtracker, ambari server, and ambari agent

Fixes: bug #1207850

Change-Id: I76719430d75cb2c3b00c4dd63190659ca8046efb
(cherry picked from commit cd27739bf172fccf0857f49ce5314a7b4e98c748)
Merge "Added validation checks to HDP plugin" into stable/0.2