[ale] Rotation can handle mixed compressed and uncompressed logs.

Change-Id: Iec10c49e3d4953265cca7eff26b65d0907f321ed
Reviewed-on: http://review.couchbase.org/37941
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>