Avoid Unnecessary Autoboxing & Allocations

[amcrn]

• KeyUtil.getKeyBytes(String) was being called twice for every Key,
  causing unnecessary byte[] allocations.
• flags is more often than not 0, therefore send 0 as a String vs.
  an int to avoid autoboxing the int to an Integer and requiring
  unnecessary String.valueOf(Integer) + Integer.toString()
  allocations.
• exp is commonly 0 (for never expire), and therefore send 0 as a
  String vs. an int to avoid the same issue mentioned above for
  flags.

If flags is 0 and exp is 0, ~10% less garbage is allocated as a
result of this optimization.