osbuilder: fix alpine agent build

Since we always build musl kata-agent, there is no need to build
it inside a musl container. We can just build on the host and then
copy the binary to the target rootfs.

There are still a lot to clean up and it should be made so for ALL
target distros instead of just alpine. But this is at least working
for alpine first.

Signed-off-by: Peng Tao <bergwolf@hyper.sh>

tools/packaging/kernel/configs/fragments/whitelist.conf

@@ -7,3 +7,4 @@ CONFIG_NF_NAT_PROTO_GRE
 CONFIG_NF_NAT_PROTO_SCTP
 CONFIG_NF_NAT_PROTO_UDPLITE
 CONFIG_REFCOUNT_FULL
+CONFIG_MEMCG_SWAP_ENABLED