1. Support loading Priam properties in this order:

  a. SimpleDB
  b. Priam.properties in classpath
  c. Java's command line (-Da=b)
  d. Default value in PriamConfiguration.java

2. Also, fix a bug in loading CassandraProcessManager through Google Guice that we did not load it in the last check-in

3. Print out the cassandra launching script's output because checking the script's exit code is not enough to detect a failed start
   With this, the priam.log will tell the problem to help users.  Best way is to fix our code to detect.