.travis.yml, scripts: Fix minor bugs in the test script.

1. setting environment variable cannot be in quote
2. "--race" testing for unit tests is supposed to be part of linux-amd64-unit-4-cpu-race config.
3. 'run' function in test script should log_error in case of failed
command (wrong operator for ints comparison in bash).

scripts/test_lib.sh

@@ -72,7 +72,7 @@ function run {
   log_callout "% ${repro}"
   "${@}"
   local error_code=$?
-  if [ ${error_code} != 0 ]; then
+  if [ ${error_code} -ne 0 ]; then
     log_error -e "FAIL: (code:${error_code}):\n  % ${repro}"
     return ${error_code}
   fi