Try to use PSETEX when possible

In order to provide more accurate heartbeating expiry we should
try to use the PSETEX command when we can (which supports millisecond
resolution expiry instead of using the SETEX which only supports
second level expiry).

Change-Id: I4f6e6b20ec26d9da03caf508c8e6b4c54c156f93
Merge "Try to use PSETEX when possible"