Increase test retries to 10 (basically infinite).

This basically means: try until you run out of time (50 minutes on
Travis). On Linux, we really want the tests to pass, so there is no point
in limiting the number of retries. On windows, we don't retry, on FreeBSD
it's limited to 1.

other/travis/env.sh

@@ -11,7 +11,7 @@ export CMAKE_EXTRA_FLAGS="-DERROR_ON_WARNING=ON -DBUILD_NTOX=ON"
 export MAKE=make
 
 BUILD_DIR=_build
-MAX_TEST_RETRIES=3
+MAX_TEST_RETRIES=10
 
 # Workaround for broken Travis image.
 export TERM=xterm