feature(session_info): print last_zxid as hex
feature(session_info): print last_zxid as hex

The zxid is composed of 64 bits, of which the highest
32 are the epoch (i.e.: they mark the start of new
leader) and the lower 32 are the transactions counter
for that epoch.

Signed-off-by: Raul Gutierrez S <f25f6873bbbde69f1fe653b3e6bd40d543b8d0e0@itevenworks.net>

rgs1/zk_shell,harlowja/zk_shell,harlowja/zk_shell,rgs1/zk_shell