Rename travis-ci/ directory to ci/

We are no longer using Travis. As such, we should move away from a lot
of CI functionality located in a folder called travis-ci/. This change
renames the travis-ci/ directory to the more generic ci/.
To preserve backwards compatibility until all "consumers" have
transitioned, we add a symbolic link called travis-ci back. It will be
removed in the near term future.

Signed-off-by: Daniel Müller <deso@posteo.net>

ci/managers/test_compile.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+set -euox pipefail
+
+EXTRA_CFLAGS=${EXTRA_CFLAGS:-}
+EXTRA_LDFLAGS=${EXTRA_LDFLAGS:-}
+
+cat << EOF > main.c
+#include <bpf/libbpf.h>
+int main() {
+  return bpf_object__open(0) < 0;
+}
+EOF
+
+# static linking
+${CC:-cc} ${EXTRA_CFLAGS} ${EXTRA_LDFLAGS} -o main -I./include/uapi -I./install/usr/include main.c ./build/libbpf.a -lelf -lz