Add a timeout parameter for reboot

[guazhang]

the default reboot timeout is 5min, it's not enough for heavy server.
Hit a error like below.

12:06:12 Reboot during test '/kdump/setup-nfsdump' with reboot count 1.
...
12:13:26 wait: 'check_boot_time' finished successfully but took too much time, 130.47 over quota
12:13:26 Connection to guest failed after reboot.
12:13:26 00:00:20 errr /kdump/setup-nfsdump (on s1) (reboot timeout) [1/3]

so maybe we need a var to extend the timeout, like TMT_REBOOT_TIMEOUT=600

[happz]

https://github.com/teemtee/tmt/blob/main/tmt/steps/provision/__init__.py#L1574 - it's either a timeout, extracted from a reboot request file, or the default. Tests don't bother with their custom timeouts, and why would they, and the default cannot be changed. A way to define custom default for the whole tmt run would be nice.

[rh-mcermak]

Hypothetically it might make sense to allow customizing the timeout by hostname. Maybe it'd be overengineering, dunno.

[happz]

At the meeting it was agreed we'd:

• add an environment variable to allow the user to change the default, and
• bump the default value to 10 minutes.