Ignore failure to save hns endpoint to store

[msabansal]

Workaround for #1950 to treat failure to save endpoint to store as non fatal. These endpoints are just required for cleanup in case of docker service crash and saving them is not really required and should not be considered fatal.

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "savefail" git@github.com:msabansal/libnetwork.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[codecov-io]

Codecov Report

Merging #1951 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1951      +/-   ##
==========================================
- Coverage      38%   37.99%   -0.01%     
==========================================
  Files         137      137              
  Lines       27149    27149              
==========================================
- Hits        10317    10315       -2     
- Misses      15562    15563       +1     
- Partials     1270     1271       +1

Impacted Files	Coverage Δ
cmd/proxy/udp_proxy.go	60.82% <0%> (-9.28%)	⬇️
networkdb/cluster.go	46.73% <0%> (+0.61%)	⬆️
cmd/proxy/tcp_proxy.go	82.69% <0%> (+1.92%)	⬆️
endpoint_cnt.go	86.08% <0%> (+2.6%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c34e58a...6ea478c. Read the comment docs.

[mavenugo]

LGTM