srm: Use ISO 8601 format for transition time stamp with millisecond resolution

While debugging some issues at NDGF, I was frustrated by the lack of
precision in the timestamp of SRM transitions. Turns out the timestamps
are stored with millisecond precision, it's just the formatting doesn't
include milliseconds.

This patch switches the format to ISO 8601 compliant timestamps with
milliseconds.

Also turned on transition logging in system-test.

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Paul Millar <paul.millar@desy.de>
Acked-by: Dmitry Litvintsev <litvinse@fnal.gov>
Patch: http://rb.dcache.org/r/5892/