debug_utilities: Create ast_loggrabber

ast_loggrabber gathers log files from customizable search patterns,
optionally converts POSIX timestamps to a readable format and
tarballs the results.

Also a few tweaks were made to ast_coredumper.

Change-Id: I8bfe1468ada24c1344ce4abab7b002a59a659495
(cherry picked from commit c70915287837704090d75f181525765de7a17221)