Tidy / regularize shell command help text

Tidy / regularize shell command help text for the various shell
commands associated with time / time zone detection. This information
will be used by manual testers and CTS tests.

This commit moves some information about device_config flags to
TimeZoneDetectorShellCommand, where it relates to actual commands.

This moves the printing logic to generally use printf + \n since it
makes it easier to read the code than a mix of println / printf
statements.

Testing:

Manual inspection of...
adb shell cmd time_detector
adb shell cmd time_zone_detector
adb shell cmd location_time_zone_manager

Bug: 172229867
Bug: 184947690
Bug: 172820087
Test: See above
Change-Id: Ic4e6d30a63f980e6da08ba762327fcd0477a732d