First cut impl. for UserGroupInformation.go
saving AmRmToken for current user
first cut TOKEN(DIGEST-MD5) implementation for unmanaged AM/RM communication.
Merge pull request #1 from sidharta-s/simple-auth-sasl

first cut TOKEN(DIGEST-MD5) implementation
Merge pull request #6 from sidharta-s/master

first cut TOKEN(DIGEST-MD5) implementation