Add diskimage-builder to the list of libraries

Add diskimage-builder to the list of libraries so it can be installed
from source to be tested in gate.

Change-Id: I6cefac1eb4ebf0196a6b4d4bfc038c00921f0d70
diff --git a/tests/test_libs_from_pypi.sh b/tests/test_libs_from_pypi.sh
index f31560a..52d7426 100755
--- a/tests/test_libs_from_pypi.sh
+++ b/tests/test_libs_from_pypi.sh
@@ -42,6 +42,7 @@
 ALL_LIBS+=" debtcollector os-brick automaton futurist oslo.service"
 ALL_LIBS+=" oslo.cache oslo.reports"
 ALL_LIBS+=" keystoneauth ironic-lib oslo.privsep"
+ALL_LIBS+=" diskimage-builder"
 
 # Generate the above list with
 # echo ${!GITREPO[@]}