Merge ~cjohnston/charm-telegraf:lp2016430 into charm-telegraf:master

[Chris Johnston]

Don't require telegraf package on snap install.

LP: #2016430

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[🤖 prod-jenkaas-bootstack (prod-jenkaas-bootstack)]

PASSED: Continuous integration, rev:9a327929c307042da209a82559238954ea9b3720
https://jenkins.canonical.com/bootstack/job/lp-charm-telegraf-ci/8/
Executed test runs:
    SUCCESS: https://jenkins.canonical.com/bootstack/job/lp-charm-test-functest/667/
    None: https://jenkins.canonical.com/bootstack/job/lp-update-mp/223/

Click here to trigger a rebuild:
https://jenkins.canonical.com/bootstack/job/lp-charm-telegraf-ci/8//rebuild

review: Approve (continuous-integration)

[Eric Chen (eric-chen)]

LGTM

review: Approve

[Ramesh Sattaru (rameshcan)]

review: Approve

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision 8daf9839c74bedf7bec0bcfb1eeeda80c094436a

diff --git a/src/reactive/telegraf.py b/src/reactive/telegraf.py
index 8f88df8..6189fa3 100644
--- a/src/reactive/telegraf.py
+++ b/src/reactive/telegraf.py
@@ -972,7 +972,8 @@ def install_telegraf():
             pass
         apt.queue_install(["telegraf"])
     elif install_method == "snap":
-        apt.purge("telegraf")
+        if fetch.get_installed_version("telegraf"):
+            apt.purge("telegraf")
         config = hookenv.config()
         snap_channel = config.get("snap_channel")
         snap.install("telegraf", channel=snap_channel, classic=True)
diff --git a/src/tests/functional/tests/bundles/base-snap.yaml b/src/tests/functional/tests/bundles/base-snap.yaml
index 139ab02..6213696 100644
--- a/src/tests/functional/tests/bundles/base-snap.yaml
+++ b/src/tests/functional/tests/bundles/base-snap.yaml
@@ -3,6 +3,8 @@ applications:
     num_units: 0
     options:
       install_method: 'snap'
+      install_sources: ''
+      install_keys: ''
   ubuntu:
     charm: ch:ubuntu
     num_units: 1