HADOOP-9853: Release Dr. Elephant v0.6.6
HADOOP-9853: Release Dr. Elephant v0.6.6

snithish/dr-elephant,shankar37/dr-elephant,shankar37/dr-elephant,bretlowery/dr-elephant-mapr,nntnag17/dr-elephant-1,bretlowery/dr-elephant-mapr,bretlowery/dr-elephant-mapr,qubole/dr-elephant,shankar37/dr-elephant,nntnag17/dr-elephant-1,qubole/dr-elephant,snithish/dr-elephant,qubole/dr-elephant,snithish/dr-elephant,nntnag17/dr-elephant-1,qubole/dr-elephant,shankar37/dr-elephant,snithish/dr-elephant,nntnag17/dr-elephant-1,bretlowery/dr-elephant-mapr