Added non-zero exit code to run_bots if there is no bots to actually run

[NecroKote]

Nice addition to #76

• bot registration now raises BotRegistrationFailed if there are dependencies missing.
• at launch, the user can see all the configured bots that failed to register as log warning
• run_bots now exits with code 1 if were were no actual bots to run. this way systemd (or supervisord) status will show whether there is something wrong with bots on the start
• renamed test_bots to test_bot_telegram and made it conditional on the required package. this helps to pass tests on build servers without installing additional dependencies.

(duplicate of #77, as for some reason it didn't pull latest commit)

[coveralls]

Pull Request Test Coverage Report for Build 1800466733

• 17 of 18 (94.44%) changed or added relevant lines in 4 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+1.6%) to 69.258%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
torrt/toolbox.py	12	13	92.31%

Files with Coverage Reduction	New Missed Lines	%
torrt/utils.py	1	87.21%

Totals
Change from base Build 1798299692:	1.6%
Covered Lines:	1158
Relevant Lines:	1672

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💛 - Coveralls

[NecroKote]

@idlesign I think this one is done. Please review it again.

I've added a bunch of tests for new logic:

• magic-mock for everything telegram-lib related
• basic run_bots cycle (basically same test as before)
• test_no_bots_to_run_exists checks that in deed, sys.exit(1) occurs on torrt run_bots without having a single configured bot
• test_telegram_without_plugin_raises_exception basic check, that telegram behaves as we expect (raises BotRegistrationFailed)
• test_bot_configured_but_unregistered checks that the user sees a new warning, about configured, but unregistered bot (for example - forgot to install plugin. this happens to me all the time)

PS: Python 3.6 failing because of dependency shift. I'll prepare basic 'housekeeping' PR - shifting dates to 2022, removing 3.6 support etc..

[idlesign]

Thank you. Merged.