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/osbuilder/rootfs-builder/alpine/rootfs_lib.sh

@@ -9,8 +9,6 @@
 #
 # - Optional environment variables
 #
-# EXTRA_PKGS: Variable to add extra PKGS provided by the user
-#
 # BIN_AGENT: Name of the Kata-Agent binary
 #
 # Any other configuration variable for a specific distro must be added
@@ -24,21 +22,12 @@ build_rootfs() {
 	# Mandatory
 	local ROOTFS_DIR=$1
 
-	# In case of support EXTRA packages, use it to allow
-	# users add more packages to the base rootfs
-	local EXTRA_PKGS=${EXTRA_PKGS:-}
-
 	# Populate ROOTFS_DIR
 	check_root
 	mkdir -p "${ROOTFS_DIR}"
 
-	/sbin/apk.static \
-	    -X ${MIRROR}/${OS_VERSION}/main \
-	    -U \
-	    --allow-untrusted \
-	    --root ${ROOTFS_DIR}\
-	    --initdb add ${BASE_PACKAGES} ${EXTRA_PKGS} ${PACKAGES}
+	cp -a -r /bin /etc /lib /sbin /usr /var ${ROOTFS_DIR}
+	mkdir -p ${ROOTFS_DIR}{/root,/proc,/dev,/home,/media,/mnt,/opt,/run,/srv,/sys,/tmp}
 
-	mkdir -p ${ROOTFS_DIR}{/root,/etc/apk,/proc}
 	echo "${MIRROR}/${OS_VERSION}/main" >  ${ROOTFS_DIR}/etc/apk/repositories
 }