ci: clean up .travis.yaml

Clean up Travis CI config, extract multi-step initializations into scripts.
Also, move kernel-building tests to happen last to not block lightweight
Debian and Ubuntu tests.

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

travis-ci/vmtest/run_vmtest.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+set -eux
+
+VMTEST_SETUPCMD="PROJECT_NAME=${PROJECT_NAME} ./${PROJECT_NAME}/travis-ci/vmtest/run_selftests.sh"
+
+echo "KERNEL: $KERNEL"
+
+# Install required packages
+wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
+echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-10 main" | sudo tee -a /etc/apt/sources.list
+echo "deb http://archive.ubuntu.com/ubuntu eoan main restricted universe multiverse" | sudo tee -a /etc/apt/sources.list
+sudo apt-get -qq update
+sudo apt-get -y install dwarves=1.15-1
+sudo apt-get -qq -y install clang-10 lld-10 llvm-10
+
+# Build selftests (and latest kernel, if necessary)
+KERNEL="${KERNEL}" ${VMTEST_ROOT}/prepare_selftests.sh travis-ci/vmtest/bpf-next
+
+# Escape whitespace characters.
+setup_cmd=$(sed 's/\([[:space:]]\)/\\\1/g' <<< "${VMTEST_SETUPCMD}")
+
+if [[ "${KERNEL}" = 'LATEST' ]]; then
+  sudo -E sudo -E -u "${USER}" "${VMTEST_ROOT}/run.sh" -b travis-ci/vmtest/bpf-next -o -d ~ -s "${setup_cmd}" ~/root.img;
+else
+  sudo -E sudo -E -u "${USER}" "${VMTEST_ROOT}/run.sh" -k "${KERNEL}*" -o -d ~ -s "${setup_cmd}" ~/root.img;
+fi