qemu-arm: Set default board as mps2-an385 to get more flash for tests.

And use Ubuntu bionic for qemu-arm Travic CI job.

.travis.yml

@@ -66,6 +66,7 @@ jobs:
 
     # qemu-arm port
     - stage: test
+      dist: bionic # needed for more recent version of qemu-system-arm with mps2-an385 target
       env: NAME="qemu-arm port build and tests"
       install:
         - sudo apt-get install gcc-arm-none-eabi

ports/qemu-arm/Makefile

@@ -7,7 +7,7 @@ QSTR_DEFS = qstrdefsport.h
 # include py core make definitions
 include $(TOP)/py/py.mk
 
-BOARD ?= netduino2
+BOARD ?= mps2-an385
 
 ifeq ($(BOARD),netduino2)
 CFLAGS += -mthumb -mcpu=cortex-m3 -mfloat-abi=soft