Check value of mythfilldatabase log path before using

[sphery <mtdean@…>]

The attached patch performs several checks on the value of mythfilldatabase log path before using it to call mythfilldatabase. Currently, if the user specifies an invalid value (a directory, an unwritable file, or a file in a non-existent directory), the mythfilldatabase run fails when the shell is unable to set up stdout/stderr.

The attached patch checks for invalid values and does its best to correct them:

• If the user specifies the path of an existing filesystem object, verify that it's writable and if not disable logging with an error message in mythbackend's log file.
• If the writable filesystem object is a directory, append "/mythfilldatabase.log" and verify that the new "default" file within that directory will be writable. If not, disable logging with an error message in mythbackend's log file.
• If the user specifies the path of a non-existent filesystem object, treat it as a file path and verify that the directory path exists and is writable. If not, disable logging with an error message in mythbackend's log file.

Even when logging is disabled by the above checks, mythfilldatabase will run (as if the user did not provide a value for mythfilldatabase log path), so the patch attempts to fail-safely in all situations. It should handle any value the user may provide.

Although this does obviate the need to specify the name of a valid file for mythfilldatabase log path, I still recommend applying the patch in #3474 as it better explains that the user /can/ specify a file path for mythfilldatabase log path.

[Anduin Withers]

(In [13508]) Closes #3474, #3475

Tanks to Michael T. Dean for these patches. I've modified them slightly so any bugs introduced are my own.

Allow the mythfilldatabase log location the housekeeper uses to point to a file or a directory. Prior to this commit a directory in this setting would cause the housekeeper run mythfilldatabase to fail.