Improve make program used by nightly.
Improve make program used by nightly.

Update nightly to find make program by looking at $CHPL_NIGHTLY_MAKE in
environment, then $MAKE in environment, and finally calling chpl_make.py
script.

Previously, it was defaulting to "make", which will not work on some
platforms.

hildeth/chapel,hildeth/chapel,chizarlicious/chapel,chizarlicious/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,hildeth/chapel,CoryMcCartan/chapel,hildeth/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,chizarlicious/chapel,CoryMcCartan/chapel,hildeth/chapel,chizarlicious/chapel,hildeth/chapel,hildeth/chapel,CoryMcCartan/chapel,chizarlicious/chapel,chizarlicious/chapel,chizarlicious/chapel