tests: disable interfaces-network-control-tuntap

[zyga]

The test is randomly failing on master. We've seen failures on Debian
and on Ubuntu 16.04. The reason is unclear. I'm disabling the test per
jdstrand's request to investigate.

Signed-off-by: Zygmunt Krynicki zygmunt.krynicki@canonical.com

[jdstrand]

I'll look into the failure.

[codecov-io]

Codecov Report

Merging #4226 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4226      +/-   ##
==========================================
- Coverage   75.87%   75.87%   -0.01%     
==========================================
  Files         440      440              
  Lines       38276    38273       -3     
==========================================
- Hits        29042    29039       -3     
  Misses       7220     7220              
  Partials     2014     2014

Impacted Files	Coverage Δ
cmd/snap-update-ns/bootstrap.go	85.36% <0%> (-1%)	⬇️
interfaces/builtin/time_control.go	100% <0%> (ø)	⬆️
interfaces/builtin/timezone_control.go	100% <0%> (ø)	⬆️
interfaces/builtin/timeserver_control.go	100% <0%> (ø)	⬆️

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