Fixes pm2 not flushing logs

[Sailboat265]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	not ran
Fixed tickets	#5529
License	MIT
Doc PR	N/A

What's this PR about?

This PR aims to fix and restore the ability to use either pm2 flush <app_id> or pm2 flush <app_name> to flush logs successfully.

Why so many commits?

In the first commit of this PR, I used a regex to extract a valid filename from a log path to allow the existing if-else comparison to continue working whatever it's intended.

It worked perfectly. Well only if the user didn't seek to customize their logging path or name! Because it's found out later that this solution isn't feasible as it would mean that a log file must end with an extension of .log, or else the flush will not work.

An example is when a user tries to redirect stderr to a file like ~/myApp/logs/process.error, the solution will not be able to handle this. Hence, I have chosen to revert the changes made by the first commit.

About the latest commit

Now, about the latest commit of this PR. The printout msg of flushing a log file has been moved inside their respective if block. This fixed a problem where users are reporting that the command is printing out the log file message like below even though the logs aren't even getting flushed.

[PM2] Flushing:
[PM2] /home/pi/.pm2/logs/My-App-out.log
[PM2] /home/pi/.pm2/logs/My-App-error.log
[PM2] Logs flushed

And I don't really get what's this if-else trying to accomplish within its logic comparison.

if (l.pm2_env.pm_out_log_path.lastIndexOf('/') < l.pm2_env.pm_out_log_path.lastIndexOf(api)) {
    <...>
}

Anyways, we will be replacing it and use fs.existsSync(FILE_PATH) to check whether a log file exists or not. So now, part of the code looks like this:

if (fs.existsSync(l.pm2_env.pm_out_log_path)) {
    Common.printOut(cst.PREFIX_MSG + l.pm2_env.pm_out_log_path);
    fs.closeSync(fs.openSync(l.pm2_env.pm_out_log_path, 'w'));
}

This solution should be universal enough that it allows the command to flush the logs correctly even though a unique log path has been specified.

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[Sailboat265]

This pull request is too polluted and it seems like I didn't adhere to the CONTRIBUTING rules too.

Hence, I have decided to move to a new PR, #5533.