Update Elxr specific changes

test case:

build python-apt, and generate python-apt-common_2.6.0-1+elxr3_all.deb
boot edge image in qemu, and copy python-apt-common_2.6.0-1+elxr3_all.deb in qemu
in qemu:
apt install software-properties-common
apt install python3-apt
dpkg -i python-apt-common_2.6.0-1+elxr3_all.deb in qemu
apt-add-repository -L

Fix the following error:

apt-add-repository -L
Traceback (most recent call last):
  File "/usr/bin/apt-add-repository", line 361, in <module>
    addaptrepo = AddAptRepository()
                 ^^^^^^^^^^^^^^^^^^
  File "/usr/bin/apt-add-repository", line 39, in __init__
    self.distro.get_sources(self.sourceslist)
  File "/usr/lib/python3/dist-packages/aptsources/distro.py", line 89, in get_sources
    raise NoDistroTemplateException(
aptsources.distro.NoDistroTemplateException: Error: could not find a distribution template for Elxr/aria
WARNING: "apt-add-repository -L" returns 1

The Elxr and aria comes from /etc/os-release

root@localhost:~# grep -e "^VERSION_CODENAME" -e "^ID" /etc/os-release
VERSION_CODENAME=aria
ID=elxr

Signed-off-by: Li Wang li.wang@windriver.com