tests: For pyboard, add test for I2C error handling and recovery.

tests/pyb/i2c_error.py

+# test I2C errors, with polling (disabled irqs) and DMA
+
+import pyb
+from pyb import I2C
+
+# init accelerometer
+pyb.Accel()
+
+# get I2C bus
+i2c = I2C(1, I2C.MASTER) 
+
+# test polling mem_read
+pyb.disable_irq()
+i2c.mem_read(1, 76, 0x0a) # should succeed
+pyb.enable_irq()
+try:
+    pyb.disable_irq()
+    i2c.mem_read(1, 77, 0x0a) # should fail
+except OSError as e:
+    pyb.enable_irq()
+    print(repr(e))
+i2c.mem_read(1, 76, 0x0a) # should succeed
+
+# test polling mem_write
+pyb.disable_irq()
+i2c.mem_write(1, 76, 0x0a) # should succeed
+pyb.enable_irq()
+try:
+    pyb.disable_irq()
+    i2c.mem_write(1, 77, 0x0a) # should fail
+except OSError as e:
+    pyb.enable_irq()
+    print(repr(e))
+i2c.mem_write(1, 76, 0x0a) # should succeed
+
+# test DMA mem_read
+i2c.mem_read(1, 76, 0x0a) # should succeed
+try:
+    i2c.mem_read(1, 77, 0x0a) # should fail
+except OSError as e:
+    print(repr(e))
+i2c.mem_read(1, 76, 0x0a) # should succeed
+
+# test DMA mem_write
+i2c.mem_write(1, 76, 0x0a) # should succeed
+try:
+    i2c.mem_write(1, 77, 0x0a) # should fail
+except OSError as e:
+    print(repr(e))
+i2c.mem_write(1, 76, 0x0a) # should succeed

tests/pyb/i2c_error.py.exp

+OSError(5,)
+OSError(5,)
+OSError(5,)
+OSError(5,)