test/hook.py. Add human-friendly annotations to log msgs.

test/hook.py.  Add human-friendly annotations to log msgs.

*  Add human-friendly annotations to packed data values in
   the logs.

Examples:
vpp-unittest-TestNAT66-_JdbMS/log.txt:22:31:29,152 API: ip_neighbor_add_del (is_static=0, is_no_adj_fib=0, is_add=1, sw_if_index=2, dst_address='\xfd\x01\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02 (fd01:2::2)', mac_address='\x02\x02\x00\x00\xff\x02 (02:02:00:00:ff:02)', is_ipv6=1)

vpp-unittest-TestACL_dot1ad_bridged-xEdhrj/log.txt:22:31:17,130 API: ip_neighbor_add_del (is_static=0, is_no_adj_fib=0, is_add=1, sw_if_index=5, dst_address='\xfd\x01\x00\x05\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xc9 (fd01:5::c9)', mac_address='\x02\x05\xc9\x00\xff\xc9 (02:05:c9:00:ff:c9)', is_ipv6=1)
vpp-unittest-TestACL_dot1ad_bridged-xEdhrj/log.txt:22:31:17,240 API: sw_interface_add_del_address (address_length=24, del_all=0, is_add=1, sw_if_index=6, address='\xac\x10\x06\x01 (172.16.6.1)', is_ipv6=0)
vpp-unittest-TestACL_dot1ad_bridged-xEdhrj/log.txt:22:31:17,314 API: sw_interface_add_del_address (address_length=64, del_all=0, is_add=1, sw_if_index=6, address='\xfd\x01\x00\x06\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01 (fd01:6::1)', is_ipv6=1)

Change-Id: Id6991569ee0ff853f76fae8fac941e8a26468a19
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>