[docker] simplify the log handling of sshd

[das7pad]

By default sshd forwards any log messages to the syslog. As docker containers do not have access to the syslog daemon on the docker-host, a new daemon was added into the container gogs/gogs#1898.

This indirection is actually not needed. We can get the log messages directly into the docker container log.

Using the -e flag for sshd forwards the output to stderr and with a stream redirect we can get the output to stdout.

Startup and invalid auth before and after applying this patch:

# docker logs --timestamps gitea_container_syslogd | grep -e ' Server listening' -e ' user'
2019-04-06T18:15:29.117905987Z Apr  6 18:15:29 sshd[72]: Server listening on :: port 22.
2019-04-06T18:15:29.117945956Z Apr  6 18:15:29 sshd[72]: Server listening on 0.0.0.0 port 22.
2019-04-06T18:18:43.162626992Z Apr  6 18:18:43 sshd[84]: Connection closed by invalid user nobody 172.x.x.x port 39836 [preauth]

# docker logs --timestamps gitea_container_direct | grep -e ' Server listening' -e ' user'
2019-04-06T18:30:01.538122152Z Server listening on :: port 22.
2019-04-06T18:30:01.538175245Z Server listening on 0.0.0.0 port 22.
2019-04-06T18:30:41.454457822Z Connection closed by invalid user nobody 172.x.x.x port 41812 [preauth]

[codecov-io]

Codecov Report

Merging #6529 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6529      +/-   ##
==========================================
+ Coverage   40.54%   40.54%   +<.01%     
==========================================
  Files         406      406              
  Lines       54501    54501              
==========================================
+ Hits        22095    22098       +3     
+ Misses      29370    29367       -3     
  Partials     3036     3036

Impacted Files	Coverage Δ
modules/log/event.go	65.98% <0%> (+1.52%)	⬆️

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