conditionally set MAX_ARRAY_BYTES if not already set

Author: rerpha

src/genie_python/genie.py

@@ -14,7 +14,10 @@
 
 from genie_python.genie_api_setup import __api as _genie_api
 
-os.environ["EPICS_CA_MAX_ARRAY_BYTES"] = "20000000"
+EPICS_CA_MAX_ARRAY_BYTES = "EPICS_CA_MAX_ARRAY_BYTES"
+if EPICS_CA_MAX_ARRAY_BYTES not in os.environ:
+    os.environ[EPICS_CA_MAX_ARRAY_BYTES] = "20000000"
+
 os.environ["FROM_IBEX"] = str(False)
 
 # for user import this functionality so they can do g.adv and g.sim