Merge ~jason-hobbs/layer-snap:fix-1843745 into ~stub/layer-snap:master

[Jason Hobbs]

Don't use universal_newlines with subprocess.

This causes decode errors when the locale is ascii, which is
the default and is used in the juju hook context where no
locale is set.

LP: #1843745

We fixed a similar issue in the past; you can see the discussion for it here:

https://code.launchpad.net/~jason-hobbs/layer-snap/+git/layer-snap/+merge/366424

Here's what the output looks like with this fix:

2019-09-12 19:07:33 INFO juju-log Installing grafana from store
2019-09-12 19:08:04 DEBUG juju-log Installation successful cmd="['snap', 'install', '--channel=stable', 'grafana']" output="b'2019-09-12T19:07:54Z INFO Waiting for restart...\ngrafana 5.0.0 from Alvaro Ur\xc3\xada (aluria) installed\n'"

[Stuart Bishop (stub)]

Yup

review: Approve

diff --git a/lib/charms/layer/snap.py b/lib/charms/layer/snap.py
index 4929abe..88557aa 100644
--- a/lib/charms/layer/snap.py
+++ b/lib/charms/layer/snap.py
@@ -313,8 +313,7 @@ def _install_store(snapname, **kw):
     cmd.append(snapname)
     hookenv.log('Installing {} from store'.format(snapname))
     try:
-        out = subprocess.check_output(cmd, stderr=subprocess.STDOUT,
-                                      universal_newlines=True)
+        out = subprocess.check_output(cmd, stderr=subprocess.STDOUT)
         hookenv.log('Installation successful cmd="{}" output="{}"'
                     .format(cmd, out),
                     level=hookenv.DEBUG)