roachprod: move /tmp/cores files somewhere under /mnt/data1 on gce

[danhhz]

Found while looking into a roachtest failure, this is gce specific, I haven't investigated aws. These files are huge and taking most of the root partition, which then causes cascading badness. I think /mnt/data1 is basically the only place they could go:

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            7.1G     0  7.1G   0% /dev
tmpfs           1.5G  9.6M  1.4G   1% /run
/dev/sda1       9.7G  9.7G     0 100% /
tmpfs           7.1G     0  7.1G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           7.1G     0  7.1G   0% /sys/fs/cgroup
/dev/sdb        369G  425M  350G   1% /mnt/data1
tmpfs           1.5G     0  1.5G   0% /run/user/1005

[danhhz]

One of these files was 8.5G on a 9.7G root partition.

ls -l -h /tmp/cores/core.cockroach.3494.dan-1552335208-cdc-ledger-rangefeed-true-0001.1552335817
-rw------- 1 dan dan 8.5G Mar 11 20:28 /tmp/cores/core.cockroach.3494.dan-1552335208-cdc-ledger-rangefeed-true-0001.1552335817

[yuzefovich]

I ran into this problem on aws as well.