server status RPC method: deal with servers without a install server

Autotest servers without a installation server are actually a valid
deployment scenario. So, in those cases, do not set the server's
"concern" status.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
autotest-scheduller: add the dependency on mysql to the systemd service file

After a fresh install of autotest from next, I tested a new feature of arc:

$ arcli server -s
Concerns: Yes
Scheduler Running: No
Scheduler Watcher Running: Yes
Install Server Running: No
Log Disk Space Usage: 18%

Running `systemctl status autotestd` would show:

_drone_manager.shutdown()
AttributeError: 'NoneType' object has no attribute 'shutdown'
Traceback (most recent call last):
File "/usr/local/autotest/scheduler/autotest-scheduler", line 13, in <module>
monitor_db.main()
File "/usr/local/autotest/scheduler/monitor_db.py", line 279, in main
main_without_exception_handling()
File "/usr/local/autotest/scheduler/monitor_db.py", line 272, in main_without_exce...andling
_drone_manager.shutdown()
AttributeError: 'NoneType' object has no attribute 'shutdown'

Turns out that the autotestd was trying to start before the MySQL
database, which is hard dependency.

After this patch, arcli is happy about the server state:

$ arcli server -s
Concerns: No
Scheduler Running: Yes
Scheduler Watcher Running: Yes
Install Server Running: No
Log Disk Space Usage: 18%

Signed-off-by: Cleber Rosa <crosa@redhat.com>
server.hosts.remote: When install server is not available, retry

Rather than giving up and throwing a hard to understand
exception to users when the install server code can't reach
the install server, retry every install_timeout / 100 seconds.

If after install_timeout / 10 we still could not reach
the server, then throw an easier to understand error
(Could not contact the install server).

CC: Rudá Moura <rmoura@redhat.com>
Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
server.hosts.remote: Introduce default install timeout

When selecting "Reinstall" on a given machine, we'll
fail because the server side test reinstall doesn't
set a proper timeout. So when no timeout specified,
read it from the global_config.ini file.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
server.hosts.remote: Set value type for install_timeout

By default, we read values from the config system as
strings, so we have to specify we want an integer instead.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>