0.20.3-dev AMIs available

[Andrew Purtell]

Latest EC2 scripts on 0.20 branch and trunk will pull 0.20.3-dev based AMIs 
from now until 0.20.3 release. 

Please give me a chance to change src/contrib/ec2/bin/hbase-ec2-env.sh for the 
release tarball (need to drop the -dev). 

   - Andy