Provide actual reason for skipped MTR test instead of reason provided by disabled.def

If a MTR testcase;
1) Is disabled by being listed in the suite's disabled.def file
2) Is run by MTR nonetheless by using the -enable-disabled option
3) Is skipped because for example a library is missing

Then MTR will report the test as skipped '[ skipped ]' but will list the reason (directly behind the skipped notice in the output) as the reason provided in the disabled.def file, which is incorrect. The real reason is the missing library.

Workaround:
1) Remark ('#' prefix) the disabled test in the disabled.def file
2) Re-run the test with standard MTR (no need for the --enable-disabled option)
3) The real reason (for example missing library with the library's name) will now be shown in the output

Proposed fix: When a test is skipped, and --enable-disabled is active, report the real reason (for example missing library) instead of the info from the disabled.def file (which is not relevant at such point as --enable-disabled is active).