Guard against DIB_COMMON_ELEMENTS not existing

create-nodes isn't just used inside of devtest (e.g. when creating test
env hosts) so we shouldn't assume DIB_COMMON_ELEMENTS will exist.

Change-Id: Ib6c301b1bd8ba27f38a31bad679fb73e24abcca5
Merge "Guard against DIB_COMMON_ELEMENTS not existing"