local_testing: arm64 chroot setup commands fixes

1. changed "distro" on few places with "chroot_distro" only in the sbuild section for consitensy in the whole section, because at some places was used "distro" on others "chroot_distro"
2. added "--foreign" option in the sbuild setup command for arm4 because its needed for cross architecture setups
3. again for the sbuild arm64 setup commant at the end switched to the webpage to "http://ports.ubuntu.com/ubuntu-ports/" for arm64 binaries

systemdev/testing-locally.rst

@@ -109,7 +109,7 @@ Create the directory ``~/logs`` if it does not exist, yet::
 
 Creating a build chroot
 ^^^^^^^^^^^^^^^^^^^^^^^
-In order to create a chroot based on Ubuntu 20.04 (Focal Fossa) with the amd64 architecture under the directory ``/srv/chroot/ubports-${distro}-amd64`` (``chroot_base`` can be changed if needed) the following variables can be defined for later use by the actual commands::
+In order to create a chroot based on Ubuntu 20.04 (Focal Fossa) with the amd64 architecture under the directory ``/srv/chroot/ubports-${chroot_distro}-amd64`` (``chroot_base`` can be changed if needed) the following variables can be defined for later use by the actual commands::
 
     chroot_distro=focal
     chroot_base=/srv/chroot/ubports-${chroot_distro}-amd64
@@ -125,10 +125,10 @@ In both cases the chroot will be created by running the following command::
 
     sudo sbuild-createchroot --components=main,restricted,universe --extra-repository="deb http://archive.ubuntu.com/ubuntu/ ${chroot_distro}-updates main restricted universe" --include=ccache "${chroot_distro}" "${chroot_base}" http://archive.ubuntu.com/ubuntu/
 
-A chroot for cross-building arm64 packages on an amd64 host can e.g. be created under the directory ``/srv/chroot/ubports-${distro}-arm64`` using::
+A chroot for cross-building arm64 packages on an amd64 host can e.g. be created under the directory ``/srv/chroot/ubports-${chroot_distro}-arm64`` using::
 
-    chroot_base=/srv/chroot/ubports-${distro}-arm64
-    sudo sbuild-createchroot --arch=arm64 --components=main,restricted,universe --extra-repository="deb http://ports.ubuntu.com/ubuntu-ports/ ${chroot_distro}-updates main restricted universe" --include=ccache "${chroot_distro}" "${chroot_base}" http://archive.ubuntu.com/ubuntu/
+    chroot_base=/srv/chroot/ubports-${chroot_distro}-arm64
+    sudo sbuild-createchroot --arch=arm64 --foreign --components=main,restricted,universe --extra-repository="deb http://ports.ubuntu.com/ubuntu-ports/ ${chroot_distro}-updates main restricted universe" --include=ccache "${chroot_distro}" "${chroot_base}" http://ports.ubuntu.com/ubuntu-ports/
 
 For cross-building armhf packages the above command can be used with ``arm64`` changed to ``armhf``.