Re-add logdirs in whitebox scripts.

These scripts do not source common.bash, so it is not set by default. They were
accidentally removed in c2c3e9b.
Use Nightly to keep track of whitebox logs.
Merge pull request #658 from thomasvandoren/fix-wb-log-dir

Re-add logdirs in whitebox scripts.

These scripts do not source common.bash, so it is not set by default. They were
accidentally removed in c2c3e9b.