[ZEPPELIN-5989] Resolve a local notebook dir as a file path instead of parsing it as a URI

[dev-donghwan]

What is this PR for?

VFSNotebookRepo.setNotebookDirectory() parses the notebook dir with new URI() unless it is a Windows absolute path like C:\.... A local path is not a URI and can contain characters that a URI does not allow:

• On Windows the default dir is built as ./ + \ + notebook, so the server fails to start with URISyntaxException: Illegal character in path at index 2: ./\notebook.
• On any OS, a dir with a space, like /home/me/My Notebooks, fails the same way.

The issue suggests joining the dir with Paths.get, but on Windows that gives .\notebook, which new URI() rejects too.

This PR:

• Resolves a notebook dir without a scheme as a file path, new File(getAbsoluteDir(path)).toURI(), and parses only a dir with a scheme as a URI. The branch that handled a URI without a scheme is removed, since that case no longer reaches it.
• Keeps rootNotebookFolder as a decoded path for a local dir. It was the root's URI with file:/// replaced, so it kept %20 for a space. list() strips it from note file names that are decoded since ZEPPELIN-6202, which would shift note paths by two characters per space, and GitNotebookRepo opens the repository at rootNotebookFolder/.git, which would be a different directory. list() now resolves the root by its URI instead of by this path. A dir with another scheme keeps its current value.

For a local dir without such characters, both values are the same as before.

I could not run it on Windows. On other systems the same code path is reached with a space, and Commons VFS treats a backslash in the file URI as a separator. It would help if someone on Windows could start the server from this branch without a configuration file, which is how the issue reproduces it.

What type of PR is it?

Bug Fix

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-5989

How should this be tested?

• VFSNotebookRepoTest.testNotebookDirWithCharactersThatAUriDoesNotAllow uses a dir with a space and one with a backslash, saves and lists a note, and checks its path.
• GitNotebookRepoTest.notebookDirWithSpace checks that .git is created in the dir with a space and that a checkpoint is recorded.

Without the first change both tests fail with the URISyntaxException above; without the second the path and .git checks fail.

Run locally: VFSNotebookRepoTest (8), GitNotebookRepoTest (12), NotebookRepoSyncTest (10), NotebookServiceTest (13), NotebookServiceRaceConditionTest (1), NoteManagerMoveResaveRaceTest (1), NotebookTest (42). testSchedule, testScheduleDisabledWithName and testSchedulePoolUsage fail locally with and without this change: they wait five seconds for the cron run, and the interpreter process here takes about six seconds to sync its libraries and register.