There was no ability to set the mtr arguments of:
* --max-save-core; and
* --max-save-datadir

to 0. This is desireable in an automatied scenario where space
is limited hence targeting 10.1 branch.

We take away the 0 means unlimited aspect for these,
however, perl can handle some big numbers so they may as well be
close enough to unlimited for all meaningful purposes.