test: make test-fs-access stricter

Change regular expression matching in assert.throws() to match the entire error message. In assert.throws() that uses a function for matching rather than a regular expression, add checks for the message property and the error's constructor.

Also, refactored to remove unnecessary temp file handling. No need to remove temp files after the test. Each test is responsible for clearing the temp directory if it needs to use it.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

test fs