[explorer/init] Introduce special case for Syno-flavoured upstart

While Synology DSM uses upstart as init, it uses /usr/share/init (which is
symlinked to /etc/init) and has special commands to start or stop services.
3 jobs for feature/dsm-support in 1 minute and 3 seconds (queued for 26 seconds)
latest
Status Job ID Name Coverage
  Test
passed #7787
pycodestyle

00:00:17

failed #7786
shellcheck

00:00:20

passed #7788
unit_tests

00:00:25

 
Name Stage Failure
failed
shellcheck Test
Skipping Git submodules setup
Authenticating with credentials from job payload (GitLab Registry)
$ ./bin/cdist-build-helper version
$ ./bin/cdist-build-helper shellcheck
cdist/conf/explorer/os_version:67:12: note: Not following: /etc/VERSION: openBinaryFile: does not exist (No such file or directory) [SC1091]
cdist/conf/explorer/os_version:69:14: warning: productversion is referenced but not assigned. [SC2154]
cdist/conf/explorer/os_version:70:14: warning: buildnumber is referenced but not assigned. [SC2154]
cdist/conf/explorer/os_version:71:14: warning: smallfixnumber is referenced but not assigned. [SC2154]
ERROR: Job failed: exit code 1