run-unit-test-docker.sh: Use mktemp for temporary directories

Don't try to hand-roll the equivalent.

Tested: Ran /bin/bash -n on the script, parsed without failure.

Change-Id: Idb5bcd1300b4158e1cc22964003792f9658de47e
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
1 file changed