Reduce the cardinality of scap timers/statsd metrics (phase 1)

This commit plucks the low hanging fruit of the scap deploy and
scap prep timers.

log.py:

Allow the timer measurement name to be specified separately from the
description that is displayed to the user. Also allow transmission of
the measurement to be disabled by specifying a name of None.

cli.py:

Update the signature of Application.Timer() to match the changes
made to log.Timer().

deploy.py:

Specify a measurement name of deploy.

prep.py:

Specify a measurement name of prep.

Bug: T377883