Merge ~zhhuabj/layer-snap:lp1847574 into ~stub/layer-snap:master

[Hua Zhang]

python3.5 subprocess.check_output() doesn't support encoding argument according to the doc [1], so the command 'juju deploy cs:graylog-39 --config channel=3/stable --series xenial' doesn't work, this change is used to fix it.

[1] https://docs.python.org/3.5/library/subprocess.html

[Stuart Bishop (stub)]

I'd like this to be .decode('utf-8', errors='replace') while we are here, to avoid crashing if the output is not valid UTF-8.

review: Needs Fixing

[Stuart Bishop (stub)]

Easiest if I make the change while merging this.

review: Approve

diff --git a/lib/charms/layer/snap.py b/lib/charms/layer/snap.py
index 88557aa..162667c 100644
--- a/lib/charms/layer/snap.py
+++ b/lib/charms/layer/snap.py
@@ -253,7 +253,7 @@ def get_installed_version(snapname):
             'Cannot get {} snap installed version because it is not installed'
             .format(snapname), hookenv.WARNING)
         return
-    return subprocess.check_output(cmd, encoding='utf-8').partition(
+    return subprocess.check_output(cmd).decode('utf-8').partition(
         'installed:')[-1].split()[0]
 
 
@@ -268,7 +268,7 @@ def get_installed_channel(snapname):
             'Cannot get snap tracking (channel) because it is not installed'
             .format(snapname), hookenv.WARNING)
         return
-    return subprocess.check_output(cmd, encoding='utf-8').partition(
+    return subprocess.check_output(cmd).decode('utf-8').partition(
         'tracking:')[-1].split()[0]