ci: carry on after selftest failure and report test group results

Two changes come with this patch:

- Test groups report their exit status individually for the final
  summary, by appending it to /exitstatus in the VM. “Test groups” are
  test_maps, test_verifier, test_progs, and test_progs-no_alu32.

- For these separate reports to make sense, allow the CI action to carry
  on even after one of the groups fails, by adding "&& true" to the
  commands in order to neutralise the effect of the "set -e".

travis-ci/vmtest/run_selftests.sh

@@ -4,6 +4,8 @@ set -euo pipefail
 
 source $(cd $(dirname $0) && pwd)/helpers.sh
 
+STATUS_FILE=/exitstatus
+
 read_lists() {
 	(for path in "$@"; do
 		if [[ -s "$path" ]]; then
@@ -15,24 +17,31 @@ read_lists() {
 test_progs() {
 	if [[ "${KERNEL}" != '4.9.0' ]]; then
 		travis_fold start test_progs "Testing test_progs"
-		./test_progs ${BLACKLIST:+-d$BLACKLIST} ${WHITELIST:+-a$WHITELIST}
+		# "&& true" does not change the return code (it is not executed
+		# if the Python script fails), but it prevents exiting on a
+		# failure due to the "set -e".
+		./test_progs ${BLACKLIST:+-d$BLACKLIST} ${WHITELIST:+-a$WHITELIST} && true
+		echo "test_progs:$?" >> "${STATUS_FILE}"
 		travis_fold end test_progs
 	fi
 
 	travis_fold start test_progs-no_alu32 "Testing test_progs-no_alu32"
-	./test_progs-no_alu32 ${BLACKLIST:+-d$BLACKLIST} ${WHITELIST:+-a$WHITELIST}
+	./test_progs-no_alu32 ${BLACKLIST:+-d$BLACKLIST} ${WHITELIST:+-a$WHITELIST} && true
+	echo "test_progs-no_alu32:$?" >> "${STATUS_FILE}"
 	travis_fold end test_progs-no_alu32
 }
 
 test_maps() {
 	travis_fold start test_maps "Testing test_maps"
-	./test_maps
+	./test_maps && true
+	echo "test_maps:$?" >> "${STATUS_FILE}"
 	travis_fold end test_maps
 }
 
 test_verifier() {
 	travis_fold start test_verifier "Testing test_verifier"
-	./test_verifier
+	./test_verifier && true
+	echo "test_verifier:$?" >> "${STATUS_FILE}"
 	travis_fold end test_verifier
 }