Test "ubuntu-core-20-64:tests/core/netplan" is flaky

[Michael Vogt]

We see failures like:

"""
2021-11-04T02:46:01.0529339Z ##[error]2021-11-04 02:46:01 Error executing google:ubuntu-core-20-64:tests/core/netplan (nov040151-785864) :
2021-11-04T02:46:01.0580605Z -----
2021-11-04T02:46:01.0581726Z + versions='16 18 20'
2021-11-04T02:46:01.0582655Z + os.query is-pc-i386
2021-11-04T02:46:01.0583416Z + for rel in $versions
2021-11-04T02:46:01.0584834Z + snap install --dangerous netplan-snap-16.snap
2021-11-04T02:46:01.0586094Z netplan-snap 0.1 installed
2021-11-04T02:46:01.0602034Z + echo 'The interface is disconnected by default'
2021-11-04T02:46:01.0606677Z The interface is disconnected by default
2021-11-04T02:46:01.0608843Z + MATCH 'network-setup-control +netplan-snap:network-setup-control +- +-'
2021-11-04T02:46:01.0610399Z + snap connections netplan-snap
2021-11-04T02:46:01.0611855Z + echo 'Running netplan apply without network-setup-control fails'
2021-11-04T02:46:01.0613702Z Running netplan apply without network-setup-control fails
2021-11-04T02:46:01.0615375Z + netplan-snap.netplan apply
2021-11-04T02:46:01.0617147Z /snap/netplan-snap/x1/bin/netplan.sh: 6: /snap/netplan-snap/x1/bin/netplan.sh: netplan: Permission denied
2021-11-04T02:46:01.0632573Z + echo 'Count how many network service restarts happened before calling netplan apply'
2021-11-04T02:46:01.0635514Z Count how many network service restarts happened before calling netplan apply
2021-11-04T02:46:01.0637197Z ++ grep -c 'Stopped Network Service.'
2021-11-04T02:46:01.0638942Z ++ /home/gopath/src/github.com/snapcore/snapd/tests/lib/tools/journal-state get-log -u systemd-networkd
2021-11-04T02:46:01.0640158Z ++ true
2021-11-04T02:46:01.0640778Z + stopped_before=0
2021-11-04T02:46:01.0641821Z ++ grep -c 'Started Network Service.'
2021-11-04T02:46:01.0643530Z ++ /home/gopath/src/github.com/snapcore/snapd/tests/lib/tools/journal-state get-log -u systemd-networkd
2021-11-04T02:46:01.0644697Z ++ true
2021-11-04T02:46:01.0645453Z + started_before=0
2021-11-04T02:46:01.0646937Z + echo 'When the interface is connected'
2021-11-04T02:46:01.0647863Z When the interface is connected
2021-11-04T02:46:01.0649243Z + snap connect netplan-snap:network-setup-control
2021-11-04T02:46:01.0650576Z + echo 'Running netplan apply now works'
2021-11-04T02:46:01.0652010Z Running netplan apply now works
2021-11-04T02:46:01.0653348Z + netplan-snap.netplan apply
2021-11-04T02:46:01.0654339Z -----
2021-11-04T02:46:01.0654846Z .
...
2021-11-04T02:46:01.0656831Z 2021-11-04 02:46:01 Error debugging google:ubuntu-core-20-64:tests/core/netplan (nov040151-785864) : read tcp 10.21.50.84:48972->34.73.69.134:22: read: connection timed out
"""

[Ian Johnson (anonymouse67)]

Seen again:

```
Error: 2021-11-30 21:03:48 Error executing google:ubuntu-core-20-64:tests/core/netplan (nov302007-963657) :
-----
+ versions='16 18 20'
+ os.query is-pc-i386
+ for rel in $versions
+ snap install --dangerous netplan-snap-16.snap
netplan-snap 0.1 installed
+ echo 'The interface is disconnected by default'
The interface is disconnected by default
+ MATCH 'network-setup-control +netplan-snap:network-setup-control +- +-'
+ snap connections netplan-snap
+ echo 'Running netplan apply without network-setup-control fails'
Running netplan apply without network-setup-control fails
+ netplan-snap.netplan apply
/snap/netplan-snap/x1/bin/netplan.sh: 6: /snap/netplan-snap/x1/bin/netplan.sh: netplan: Permission denied
+ os.query is-core16
+ test 16 -ne 16
+ echo 'Skipping netplan generate on UC16'
Skipping netplan generate on UC16
+ echo 'Count how many network service restarts happened before calling netplan apply'
Count how many network service restarts happened before calling netplan apply
++ grep -c 'Stopped Network Service.'
++ /home/gopath/src/github.com/snapcore/snapd/tests/lib/tools/journal-state get-log -u systemd-networkd
++ true
+ stopped_before=0
++ grep -c 'Started Network Service.'
++ /home/gopath/src/github.com/snapcore/snapd/tests/lib/tools/journal-state get-log -u systemd-networkd
++ true
+ started_before=0
+ echo 'When the interface is connected'
When the interface is connected
+ snap connect netplan-snap:network-setup-control
+ echo 'Running netplan apply now works'
Running netplan apply now works
+ netplan-snap.netplan --debug apply
-----
.
2021-11-30 21:03:48 Error debugging google:ubuntu-core-20-64:tests/core/netplan (nov302007-963657) : read tcp 10.31.189.28:42640->34.139.30.74:22: read: connection timed out
```