logcat: add --id=<id> for -f option

Clear file rotate content if id signature changes. This allows
logcatd to detect change of property ro.build.id to reset the
recorded data. The id is stored in the the -f filespec as
<filespec>.id.

If the id file is missing or unreadable, do not clear. Allow an
API where chmod 0 to the id file blocks this feature. Does not
work for root.

Add logcat.logrotate_id gTest.

Bug: 30591615
Change-Id: I895749ca7c6d4af57ec57f058a29d8e3af2f8b27