Previously we only ran `fstrim` on Windows. Docker for Mac now supports
TRIM so we should run `fstrim` there too.
Note it's possible to turn off TRIM on the Mac at the virtual hardware
level via the database, but this should be harmless -- the `fstrim`
fails immediately with an obvious error if the device doesn't support it:
`fstrim: ioctl 0xc0185879 failed: Not supported`.
Signed-off-by: David Scott <dave.scott@docker.com>
See #536
This is the recommended frequency. For desktop this might be less
suitable, so we may want to adjust
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
