systemd standard unit-file is not installed correctly

[mtimm]

Please see these two PR's for what lead to this issue:

• Add systemd unit template to the RPM build #1450 - Added a parameterized systemd unit-file that required users utilize the service with an instance parameter that is then used as the port number opentsdb binds to - for example systemctl enable opentsdb@4242. Apparently this isn't documented very well and users unfamiliar with parameterized services may not know how to utilize this unit file so the next PR was added.
• Add a systemd standard opentsdb service script to launch using the port #2155 - Added a standard (non-parameterized) systemd unit-file that could be used without specifying the port number.

The problem is that #2155 makes two errors:

1. The change to Makefile.am adds systemd_file="$(top_srcdir)/build-aux/rpm/systemd/opentsdb.service" ; \ but the systemd_file variable is immediately overwritten by the next line which contains: systemd_file="$(top_srcdir)/build-aux/rpm/systemd/opentsdb@.service" ; \. This variable is then used by the next two lines and only the opentsdb@.service file is installed. It looks like the echo and install lines need to also be added for the opentsdb.service file.
2. The change to the opentsdb.spec.in file is missing the opentsdb.service file in the %files section. This results in the file not existing in the RPM and the scriptlet to attempt to link against a missing file.

Interestingly in RHEL 8 (actually I'm using AlmaLinux 8), this doesn't really cause much of an issue. Systemd seems to fallback to using a wrapper around the sysv init.d script in some way. However, in RHEL 9 (again I'm actually using AlmaLinux 9), the opentsdb systemd service shows as bad and there is no way that I have found to get it to use the sysv init.d script.

[Madhusoodan]

Are the new commits going to master?