Improve testflush, testinit and testautodetect

libarduserial/arduserial.c:
* ser_autodetect :: Improve pattern for automatic arduino serial
  detection
testsuite/arduserial/testflush.c:
* main :: made output prettier, use ser_autodetect instead of guessing
  that the arduino is on /dev/ttyACM0
* evaltest :: implement test evaluation procedure, althought don't use
  it yet
testsuite/arduserial/testinit.c:
* evaltest :: implement test evaluation procedure
* test_invalidDevice :: move test that was living in main before to its
  own procedure
* main :: use evaltest to call tests
testsuite/arduserial/testautodetect.c:
* main :: test cannot fail, only skip and pass are possible right now