ci: blacklist bpf_iter tests

Disable a bunch of new kernel selftests that can't succeed on 5.5 kernel.
Flatten Travis tests into a single stage to parallelize and speed them up.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>

.travis.yml

@@ -35,7 +35,7 @@ stages:
 
 jobs:
     include:
-        - stage: Build
+        - stage: Build & Test
           name: Debian Build
           language: bash
           install:        $CI_ROOT/managers/debian.sh SETUP
@@ -91,8 +91,7 @@ jobs:
           language: bash
           script: sudo $CI_ROOT/managers/ubuntu.sh || travis_terminate
 
-        - stage: Build & Test
-          name: Kernel 5.5.0 + selftests
+        - name: Kernel 5.5.0 + selftests
           language: bash
           env: KERNEL=5.5.0
           script:  $CI_ROOT/vmtest/run_vmtest.sh || travis_terminate