ENG-6910.  Add way to set ant arguments in build_kits.py.
Set environment variable "VOLTDB_BUILD_ARGS" to pass properties to ant.
For example: VOLTDB_BUILD_ARGS="-Dbuildstring=\"chop suey\""

(cherry picked from commit 2368200fb9d2bdfd5f2abde2b36a1a9920362654)

Conflicts:
	tools/kit_tools/build_kits.py